20. And when he was demanded of the Pharisees when the kingdom of God should come, he answered them and said, The kingdom of God comes not with observation:
21. Neither shall they say, Lo here! or, lo there! for, behold, the kingdom of God is within you.
CYRIL; Because our Savior, in His discourses which He addressed to others, spoke often of the kingdom of God, the Pharisees derided Him; hence it is said, And when he was asked by the Pharisees when the kingdom of God should come. As though they said tauntingly, "Before the kingdom of God come, which you speak of, the death of the cross will be your lot." But our Lord testifying His patience, when reviled reviles not again, but the rather because they were evil, returns not a scornful answer; for it follows, He answered and said, The kingdom comes not with observation; as if he says, "Seek not to know the time when the kingdom of heaven shall again be at hand. For that time can be observed neither by men nor angels, not as the time of the Incarnation which was proclaimed by the foretelling of Prophets and the heraldings of Angels." Wherefore He adds, Neither shall they say, Lo here! or, Lo there! Or else, They ask about the kingdom of God, because, as is said below, they thought that on our Lord's coming into Jerusalem, the kingdom of God would be immediately manifested. Therefore our Lord answers, that the kingdom of God will not come with observation.
CYRIL; Now it is only for the benefit of each individual that He says that which follows, For behold the kingdom of God is within you; that is, it rests with you and your own hearts to receive it. For every man who is justified by faith and the grace of God, and adorned with virtues, may obtain the kingdom of heaven.
GREG. NYSS.. Or, perhaps, the kingdom of God being within us, means that joy that is implanted in our hearts by the Holy Spirit. For that is, as it were, the image and pledge of the everlasting joy with which in the world to come the souls of the Saints rejoice.
BEDE; Or the kingdom of God means that He Himself is placed in the midst of them, that is, reigning in their hearts by faith.
22. And he said to the disciples, The days will come, when you shall desire to see one of the days of the Son of man, and you shall not see it.
23. And they shall say to you, See here; or, see there: go not after them, nor follow them.
24. For as the lightning, that lightens out of the one part under heaven, shines to the other part under heaven; so shall also the Son of man be in his day.
25. But first must he suffer many things, and be rejected of this generation.
CYRIL; When our Lord said, The kingdom of God is within you, He would fain prepare His disciples for suffering, that being made strong they might be able to enter the kingdom of God; He therefore foretells to them, that before His coming from heaven at the end of the world, persecution will break out upon them. Hence it follows, And he said to the disciples, The days will come, &c. meaning that so terrible will be the persecution, that they would desire to see one of His days, that is, of that time when they yet walked with Christ. Truly the Jews ofttimes beset Christ with reproaches and insults, and sought to stone Him, and ofttimes would have hurled Him down film the mountain; but even these seem to be looked upon as slight in comparison of greater evils that are to come.
THEOPHYL. For their life was then without trouble, for Christ took care of them and protected them. But the time was coming when Christ should be taken away, and they should be exposed to perils, being brought before kings and princes, and then they should long for the first time and its tranquillity.
BEDE; Or, by the day of Christ He signifies His kingdom, which we hope will come, and He lightly says, one day, because there shall no darkness disturb the glory of that blessed time. It is right then to long for the day of Christ, yet from the earnestness of our longing, let us not vision to ourselves as though the day were at hand. Hence it follows, And they shall say to you, Lo here! and, Lo there!
EUSEB. As if he said, If at the coming of Antichrist, his fame shall be spread abroad, as though Christ had appeared, go not out, nor follow him. For it cannot be that He who was once seen on earth, shall any more dwell in the corners of the earth. It will therefore be he of whom we speak, not the true Christ. For this is the clear sign of the second coming of our Savior, that suddenly the luster of His coming shall fill the whole world; and so it follows, For as the lightning that lightens, &c. For He will not appear walking upon the earth, as any common man, but will illuminate our whole universe, manifesting to all men the radiance of His divinity.
BEDE; And he well says, that lightens out of the one part under heaven, because the judgment will be given under the heaven, that is, in the midst of the air, as the Apostle says, We shall be caught up together with them in the clouds. But if the Lord shall appear at the Judgment like lightning, then shall no one remain hidden in the deep of his heart, for the very brightness of the Judge pierces through him; we may also take this answer of our Lord to refer to His coming, whereby He comes daily into His Church. For ofttimes have heretics so vexed the Church, by saying that the faith of Christ stands in their own dogma, that the faithful in those times longed that the Lord would if it were possible even for one day return to the earth, and Himself make known what was the true faith. And you shall not see it, because it need not that the Lord should again testify by a bodily presence that which has been spiritually declared by the light of the Gospel, once scattered and diffused throughout the whole world.
CYRIL; Now His disciples supposed that He would go to Jerusalem, and would at once make a manifestation of the kingdom of God. To rid them therefore of this belief, He informs them that it became Him first to suffer the Life-giving Passion, then to ascend to the Father and shine forth from above, that He might judge the world in righteousness. Hence He adds, But first must he suffer many things, and be rejected of this generation.
BEDE; He means the generation not only of the Jews, but also of all wicked men, by whom even now in His own body, that is, His Church, the Son of man suffers many things, and is rejected. But while He spoke many things of His coming in glory, He inserts something also concerning His Passion, that when men saw Him dying, whom they had heard would be glorified, they might both soothe their sorrow for His sufferings by the hope of the promised glory, and at the same time prepare themselves, if they love the glories of His kingdom, to fool; without alarm upon the horrors of death.
Catena Aurea Luke 17
Albert, the "light of Germany," called the Great because of his encyclopedic knowledge, was born in 1193 at Lauingen, Donau. He studied at Padua, where under the influence of the second Dominican general, he joined the newly-founded Order of Preachers (1223). Soon he was sent to Germany, taught in various cities, particularly Cologne; Thomas Aquinas was his student. In 1248 he received the honor of Master in Sacred Theology at Paris. Throngs attended his lectures. 
Born at Melk, Austria, he was educated by Bishop Altman of Passau and succeeded his father as margrave of Austria when he was twenty-three. He married the daughter of Emperor Henry IV, by whom he had eighteen children, in 1106, founded the monasteries of Heiligenkreuz in the Wienerwald, Klosterneuburg, near Vienriazell in Styria, and was known for his piety and charity. He refused the imperial crown when his brother-in-law Henry V died in 1125. Leopold died after reigning as margrave for forty years at Klosterneuburg. He was surnamed "the Good" by his people and was canonized in 1486. 
