From Pope St. John Paul II’s encyclical Veritatis Splendor (1993):
The conclusion of Jesus’ conversation with the rich young man is very poignant: “When the young man heard this, he went away sorrowful, for he had many possessions” (Mt 19:22). Not only the rich man but the disciples themselves are taken aback by Jesus’ call to discipleship, the demands of which transcend human aspirations and abilities: “When the disciples heard this, they were greatly astounded and said, “Then who can be saved?'” (Mt 19:25). But the Master refers them to God’s power: “With men this is impossible, but with God all things are possible” (Mt 19:26).
In the same chapter of Matthew’s Gospel (19:3-10), Jesus, interpreting the Mosaic Law on marriage, rejects the right to divorce, appealing to a “beginning” more fundamental and more authoritative than the Law of Moses: God’s original plan for mankind, a plan which man after sin has no longer been able to live up to: “For your hardness of heart Moses allowed you to divorce your wives, but from the beginning it was not so” (Mt 19:8). Jesus’ appeal to the “beginning” dismays the disciples, who remark: “If such is the case of a man with his wife, it is not expedient to marry” (Mt 19:10). And Jesus, referring specifically to the charism of celibacy “for the Kingdom of Heaven” (Mt 19:12), but stating a general rule, indicates the new and surprising possibility opened up to man by God’s grace. “He said to them: ‘Not everyone can accept this saying, but only those to whom it is given'” (Mt 19:11).
To imitate and live out the love of Christ is not possible for man by his own strength alone. He becomes capable of this love only by virtue of a gift received. As the Lord Jesus receives the love of his Father, so he in turn freely communicates that love to his disciples: “As the Father has loved me, so have I loved you; abide in my love” (Jn 15:9). Christ’s gift is his Spirit, whose first “fruit” (cf. Gal 5:22) is charity: “God’s love has been poured into our hearts through the Holy Spirit which has been given to us” (Rom 5:5). Saint Augustine asks: “Does love bring about the keeping of the commandments, or does the keeping of the commandments bring about love?” And he answers: “But who can doubt that love comes first? For the one who does not love has no reason for keeping the commandments”.29
29 In Iohannis Evangelium Tractatus, 82, 3: Corpus Christianorum, Latin series 36, 533.
— Veritatis Splendor 22