Catena Aurea by St. Thomas Aguinas
43.Ye have heard that it hath been said, Thou shalt love thy neighbour, and hate thine enemy.
44. But I say unto you, Love your enemies, bless them that curse you, do good to them that hate you, and pray for them which despitefully use you and persecute you;
45. That ye may be the children of your Father which is in heaven: for He maketh His sun to rise on the evil and on the good, and sendeth rain on the just and on the unjust.
46. For if ye love them which love you, what reward have ye? do not even the Publicans the same?
47. And if ye salute your brethren only, what do ye more than others? do not even the Publicans so?
48. Be ye therefore perfect, even as your Father which is in heaven is perfect.
GLOSS. (non occ.) The Lord has taught above that we must not resist one who offers any injury, but must be ready even to suffer more; He now further requires us to shew to them that do us wrong both love and its effects. And as the things that have gone before pertain to the completion of the righteousness of the Law, in like manner this last precept is to be referred to the completion of the law of love, which, according to the Apostle, is the fulfilling of the Law.
AUGUSTINE. (de Doctr. Christ. i. 30.) That by the command, Thou shalt love thy neighbour, all mankind were intended, the Lord shewed in the parable of the man who was left half dead, which teaches us that our neighbour is every one who may happen at any time to stand in need of our offices of mercy; and this who does not see must be denied to none, when the Lord says, Do good to them that hate you.
AUGUSTINE. (Serm. in Mont. i. 21.) That there were degrees in the righteousness of the Pharisees which was under the old Law is seen herein, that many hated even those by whom they were loved. He therefore who loves his neighbour, has ascended one degree, though as yet he hate his enemy; which is expressed in that, and shalt hate his enemy; which is not to be understood as a command to the justified, but a concession to the weak.
AUGUSTINE. (cont. Faust. xix. 24.) I ask the Manichæans why they would have this peculiar to the Mosaic Law, that was said by them of old time, thou shall hate thy enemy? Has not Paul said of certain men that they were hateful to God? We must enquire then how we may understand that, after the example of God, to whom the Apostle here affirms some men to be hateful, our enemies are to be hated; and again after the same pattern of Him who maketh his sun to rise on the evil and the good, our enemies are to be loved. Here then is the rule by which we may at once hate our enemy for the evil’s sake that is in him, that is, his iniquity, and love him for the good’s sake that is in him, that is, his rational part. This then, thus uttered by them of old, being heard, but not understood, hurried men on to the hatred of man, when they should have hated nothing but vice. Such the Lord corrects as He proceeds, saying, I say unto you, Love your enemies. Lie who had just declared that He came not to subvert the Law, bat to fulfil it, by bidding us love our enemies, brought us to the understanding of how we may at once hate the same man for his sins whom we love for his human nature.
GLOSS. (ord.) But it should be known, that in the whole body of the Law it is no where written, Thou shalt hate thy enemy. But it is to be referred to the tradition of the Scribes, who thought good to add this to the Law, because the Lord bade the children of Israel pursue their enemies, and destroy Amalek from under heaven.
PSEUDO-CHRYSOSTOM. As that, Thou shalt not lust, was not spoken to the flesh, but to the spirit, so in this the flesh indeed is not able to love its enemy, but the spirit is able; for the love and hate of the flesh is in the sense, but of the spirit is in the understanding. If then we feel hate to one who has wronged us, and yet will not to act upon that feeling, know that our flesh hates our enemy, but our soul loves him.
GREGORY. (Mor. xxii. 11.) Love to an enemy is then observed when we are not sorrowful at his success, or rejoice in his fall. We hate him whom we wish not to be bettered, and pursue with ill-wishes the prosperity of the man in whose fall we rejoice. Yet it may often happen that without any sacrifice of charity, the fall of an enemy may gladden us, and again his exaltation make us sorrowful without any suspicion of envy; when, namely, by his fall any deserving man is raised up, or by his success any undeservedly depressed. But herein a strict measure of discernment must be observed, lest in following out our own hates, we hide it from ourselves under the specious pretence of others’ benefit. We should balance how much we owe to the fall of the sinner, how much to the justice of the Judge. For when the Almighty has struck any hardened sinner, we must at once magnify His justice as Judge, and feel with the other’s suffering who perishes.
GLOSS. (ord.) They who stand against the Church oppose her in three ways; with hate, with words, and with bodily tortures. The Church on the other hand loves them, as it is here, Love your enemies; does good to them, as it is, Do good to them that hate you; and prays for them, as it is, Pray for them that persecute you and accuse you falsely.
JEROME. Many measuring the commandments of God by their own weakness, not by the strength of the saints, hold these commands for impossible, and say that it is virtue enough not to hate our enemies; but to love them is a command beyond human nature to obey. But it must be understood that Christ enjoins not impossibilities but perfection. Such was the temper of David towards Saul and Absalom; the Martyr Stephen also prayed for his enemies while they stoned him, and Paul wished himself anathema for the sake of his persecutors. (Rom. 9:3.) Jesus both taught and did the same, saying, Father, forgive them, for they know not what they do. (Luke 23:34.)
AUGUSTINE. (Enchir. 73.) These indeed are examples of the perfect sons of God; yet to this should every believer aim, and seek by prayer to God, and struggles with himself to raise his human spirit to this temper. Yet this so great blessing is not given to all those multitudes which we believe are heard when they pray, Forgive us our debts, as we forgive our debtors.
AUGUSTINE. (Serm. in Mont. i. 21.) Here arises a question, that this commandment of the Lord, by which He bids us pray for our enemies, seems opposed by many other parts of Scripture. In the Prophets are found many imprecations upon enemies; such as that in the 108th Psalm, Let his children be orphans. (Ps. 109:9.) But it should be known, that the Prophets are wont to foretel things to come in the form of a prayer or wish. This has more weight as a difficulty that John says, There is a sin unto death, I sag not that he shall pray for it; (1 John 5:16.) plainly shewing, that there are some brethren for whom he docs not bid us pray; for what went before was, If any know his brother sin a sin, &c. Yet the Lord bids us pray for our persecutors. This question can only be resolved, if we admit that there are some sins in brethren more grievous than the sin of persecution in our enemies. For thus Stephen prays for those that stoned him, because they had not yet believed on Christ; but the Apostle Paul (2 Tim. 4:14.) does not pray for Alexander though he was a brother, but had sinned by attacking the brotherhood through jealousy. But for whom you pray not, you do not therein pray against him. What must we say then of those against whom we know that the saints have prayed, and that not that they should be corrected, (for that would be rather to have prayed for them), but for their eternal damnation; not as that prayer of the Prophet against the Lord’s betrayer, for that is a prophecy of the future, not an imprecation of punishment; but as when we read in the Apocalypse the Martyrs’ prayer that they may be avenged. (Rev. 6:10.) But we ought not to let this affect us. For who may dare to affirm that they prayed against those persons themselves, and not against the kingdom of sin? For that would be both a just and a merciful avenging of the Martyrs, to overthrow that kingdom of sin, under the continuance of which they endured all those evils. And it is overthrown by correction of some, and damnation of such as abide in sin. Does not Paul seem to you to have avenged Stephen on his own body, as he speaks, (1 Cor. 9:27.) I chastise my body, and bring it into subjection.
PSEUDO-AUGUSTINE. (Hil. Quæst. V. and N. Test. q. 68.) And the souls of them that are slain cry out to be avenged; as the blood of Abel cried out of the ground not with a voice, but in spirit1. As the work is said to laud the workman, when he delights himself in the view thereof; for the saints are not so impatient as to urge on what they know will come to pass at the appointed time.
CHRYSOSTOM. Note through what steps we have now ascended hither, and how He has set us on the very pinnacle of virtue. The first step is, not to begin to do wrong to any; the second, that in avenging a wrong done to us we be content with retaliating equal; the third, to return nothing of what we have suffered; the fourth, to offer one’s self to the endurance of evil; the fifth, to be ready to suffer even more evil than the oppressor desires to inflict; the sixth, not to hate him of whom we suffer such things; the seventh, to love him; the eighth, to do him good; the ninth, to pray for him. And because the command is great, the reward proposed is also great, namely, to be made like unto God, Ye shall be the sons of your Father which is in heaven.
JEROME. For whoso keeps the commandments of God is thereby made the son of God; he then of whom he here speaks is not by nature His son, but by his own will.
AUGUSTINE. (Serm. in Mont. i. 23.) After that rule we must here understand of which John speaks, He gave them power to be made the sons of God. One is His Son by nature; we are made sons by the power which we have received; that is, so far as we fulfil those things that we are commanded. So He says not, Do these things because ye are sons; but, do these things that ye may become sons. In calling us to this then, He calls us to His likeness, for He saith, He maketh His sun to rise on the righteous and the unrighteous. By the sun we may understand not this visible, but that of which it is said, To you that fear the name of the Lord, the Sun of righteousness shall arise; (Mal. 4:2.) and by the rain, the water of the doctrine of truth; for Christ was seen, and was preached to good as well as bad.
HILARY. Or, the sun and rain have reference to the baptism with water and Spirit.
AUGUSTINE. (ubi sup.) Or we may take it of this visible sun, and of the rain by which the fruits are nourished, as the wicked mourn in the book of Wisdom, The Sun has not risen for us. (Wisd. 5:6.) And of the rain it is said, I will command the clouds that they rain not on it. (Is. 5:6.) But whether it be this or that, it is of the great goodness of God, which is set forth for our imitation. lie says not, ‘the sun,’ but, His sun, that is, the sun which Himself has made, that hence we may be admonished with how great liberality we ought to supply those things that we have not created, but have received as a boon from Him.
AUGUSTINE. (Epist. 93. 2.) But as we laud Him for His gifts, let us also consider how He chastises those whom He loves. For not every one who spares is a friend, nor every one who chastises an enemy; it is better to love with severity, than to use lenity wherewith to deceive. (vid. Prov. 27:6.)
PSEUDO-CHRYSOSTOM. He was careful to say, On the righteous and the unrighteous, and not ‘on the unrighteous as on the righteous;’ for God gives all good gifts not for men’s sake, but for the saints’ sake, as likewise chastisements for the sake of sinners. In bestowing His good gifts, He does not separate the sinners from the righteous, that they should not despair; so in His inflictions, not the righteous from sinners that they should be made proud; and that the more, since the wicked are not profited by the good things they receive, but turn them to their hurt by their evil lives; nor are the good hurt by the evil things, but rather profit to increase of righteousness.
AUGUSTINE. (De Civ. Dei, i. 8.) For the good man is not puffed up by worldly goods, nor broken by worldly calamity. But the bad man is punished in temporal losses, because he is corrupted by temporal gains. Or for another reason He would have good and evil common to both sorts of men, that good things might not be sought with vehement desire, when they were enjoyed even by the wicked; nor the evil things shamefully avoided, when even the righteous are afflicted by them.
GLOSS. (non occ.) To love one that loves us is of nature, but to love our enemy of charity. If ye love them who love you, what reward have ye? to wit, in heaven. None truly, for of such it is said, Ye have received your reward. But these things we ought to do, and not leave the other undone.
RABANUS. If then sinners be led by nature to shew kindness to those that love them, with how much greater shew of affection ought you not to embrace even those that do not love you? For it follows, Do not even the publicans so? The publicans are those who collect the public imposts; or perhaps those who pursue the public business or the gain of this world.
GLOSS. (non occ.) But if you only pray for them that are your kinsfolk, what more has your benevolence than that of the unbelieving? Salutation is a kind of prayer.
RABANUS. Ethnici, that is, the Gentiles, for the Greek word ἔθνος is translated ‘gens’ in Latin; those, that is, who abide such as they were born, to wit, under sin.
REMIGIUS. Because the utmost perfection of love cannot go beyond the love of enemies, therefore as soon as the Lord has bid us love our enemies, He proceeds, Be ye then perfect, as your Father which is in heaven is perfect. He indeed is perfect, as being omnipotent; man, as being aided by the Omnipotent. For the word ‘as’ is used in Scripture, sometimes for identity, and equality, as in that, As I was with Moses, so will I be with thee; (Josh. 1:5.) sometimes to express likeness only as here.
PSEUDO-CHRYSOSTOM. For as our sons after the flesh resemble their fathers in some part of their bodily shape, so do spiritual sons resemble their father God, in holiness.
Catena Aurea Matthew 5
From: Matthew 5:43-48
Jesus and His Teaching, the Fulfillment of the Law (Continuation)
(Jesus said to His disciples,)  "You have heard that it was said, `You shall love your neighbor and hate your enemy.'  But I say to you, Love your enemies and pray for those who persecute you.  So that you may be sons of your Father who is in Heaven; for He makes His sun rise on the evil and on the good, and sends rain on the just and on the unjust.  For if you love those who love you, what reward have you? Do not even the tax collectors do the same?  And if you salute only your brethren, what more are you doing than others? Do not even the Gentiles do the same?  You, therefore, must be perfect, as your Heavenly Father is perfect."
43. The first part of this verse--"You shall love your neighbor"--is to be found in Leviticus 19:18. The second part--"hate your enemy"—is not to be found in the Law of Moses. However, Jesus' words refer to a widespread rabbinical interpretation which understood "neighbors" as meaning "Israelites". Our Lord corrects this misinterpretation of the Law: for Him everyone is our neighbor (cf. the parable of the Good Samaritan in Luke 10:25-37).
43-47. This passage sums up the teaching which precedes it. Our Lord goes so far as to say that a Christian has no personal enemies. His only enemy is evil as such--sin--but not the sinner. Jesus Himself puts this into practice with those who crucified Him, and He continues to act in the same way towards sinners who rebel against Him and despise Him. Consequently, the saints have always followed His example--like St. Stephen, the first martyr, who prayed for those who were putting him to death. This is the apex of Christian perfection--to love, and pray for, even those who persecute us and calumniate us. It is the distinguishing mark of the children of God.
46. "Tax collectors": the Roman empire had no officials of its own for the collection of taxes: in each country it used local people for this purpose. These were free to engage agents (hence we find reference to "chief tax collectors": cf. Luke 19:2). The global amount of tax for each region was specified by the Roman authorities; the tax collectors levied more than this amount, keeping the surplus for themselves: this led them to act rather arbitrarily, which was why the people hated them. In the case of the Jews, insult was added to injury by the fact that the chosen people were being exploited by Gentiles.
48. Verse 48 is, in a sense, a summary of the teaching in this entire chapter, including the Beatitudes. Strictly speaking, it is quite impossible for a created being to be as perfect as God. What our Lord means here is that God's own perfection should be the model which every faithful Christian tries to follow, even though he realizes that there is an infinite distance between himself and his Creator. However, this does not reduce the force of this commandment; it sheds more light on it. It is a difficult commandment to live up to, but along with this we must take account of the enormous help grace gives us to go so far as to tend towards divine perfection. Certainly, perfection which we should imitate does not refer to the power and wisdom of God, which are totally beyond our scope; here the context seems to refer primarily to love and mercy. Along the same lines, St. Luke quotes these words of our Lord: "Be merciful, even as your Father is merciful" (Luke 6:36; cf. note on Luke 6:20-49).
Clearly, the "universal call to holiness" is not a recommendation but a commandment of Jesus Christ.
"Your duty is to sanctify yourself. Yes, even you. Who thinks that this task is only for priests and religious? To everyone, without exception, our Lord said: `Be ye perfect, as My Heavenly Father is perfect'" (St J. Escriva, "The Way", 291). This teaching is sanctioned by chapter 5 of Vatican II's Constitution "Lumen Gentium", where it says (40): "The Lord Jesus, divine teacher and model of all perfection, preached holiness of life (of which He is the author and maker) to each and every one of His disciples without distinction: `You, therefore, must be perfect, as your Heavenly Father is perfect' [...]. It is therefore quite clear that all Christians in any state or walk of life are called to the fullness of Christian life and to the perfection of love, and by this holiness a more human manner of life is fostered also in earthly society."
Source: Daily Word for Reflection—Navarre Bible