[6] Do not give dogs what is holy; and do not throw your pearls before swine, lest they trample them under foot and turn to attack you.
The Golden Rule
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[12] "So whatever you wish that men would do to you, do so to them; for this is the law and the prophets.
The Narrow Gate
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[13] "Enter by the narrow gate; for the gate is wide and the way is easy, that leads to destruction, and those who enter by it are many. [14] For the gate is narrow and the way is hard, that leads to life, and those who find it are few."
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Commentary:
6. Jesus uses a popular saying to teach prudent discernment in the preaching of the word of God and distribution of the means of sanctification. The Church has always heeded this warning, particularly in the sense of respect with which it administers the sacraments—especially the Holy Eucharist. Filial confidence does not exempt us from the sincere and profound respect which should imbue our relations with God and with holy things.
12. This "golden rule" gives a guideline to realize our obligations towards and the love we should have for others. However, if we interpreted it superficially it would become a selfish rule; it obviously does not mean "do utdes" ("I give you something so that you will give me something") but that we should do good to others unconditionally: we are clever enough not to put limits on how much we love ourselves. This rule of conduct will be completed by Jesus' "new commandment" (John 13:34), where He teaches us to love others as He Himself loved us.
13-14. "Enter": in St. Matthew's Gospel this verb often has as its object the "Kingdom of Heaven" or equivalent expressions (life, the marriage feast, the joy of the Lord, etc.). We can interpret "enter" as an imperious invitation.
The way of sin is momentarily pleasant and calls for no effort, but it leads to eternal perdition. Following the way of a generous and sincere Christian life is very demanding--here Jesus speaks of a narrow gate and a hard way--but it leads to Life, to eternal salvation.
The Christian way involves carrying the cross. "For if a man resolve to submit himself to carrying this cross--that is to say, if he resolve to desire in truth to meet trials and to bear them in all things for God's sake, he will find in them all great relief and sweetness wherewith he may travel upon this road, detached from all things and desiring nothing. Yet, if he desires to possess anything--whether it comes from God or from any other source--with any feeling of attachment, he has not stripped and denied himself in all things; and thus he will be unable to walk along this narrow path or climb upward by it" (St. John of the Cross, "Ascent of Mount Carmel", book 2, chapter 7, 7).