From Pope St. John Paul II’s encyclical Veritatis Splendor (1993):
Jesus’ conversation with the rich young man continues, in a sense, in every period of history, including our own. The question: “Teacher, what good must I do to have eternal life?” arises in the heart of every individual, and it is Christ alone who is capable of giving the full and definitive answer. The Teacher who expounds God’s commandments, who invites others to follow him and gives the grace for a new life, is always present and at work in our midst, as he himself promised: “Lo, I am with you always, to the close of the age” (Mt 28:20). Christ’s relevance for people of all times is shown forth in his body, which is the Church. For this reason the Lord promised his disciples the Holy Spirit, who would “bring to their remembrance” and teach them to understand his commandments (cf. Jn 14:26), and who would be the principle and constant source of a new life in the world (cf. Jn 3:5-8; Rom 8:1-13).
The moral prescriptions which God imparted in the Old Covenant, and which attained their perfection in the New and Eternal Covenant in the very person of the Son of God made man, must be faithfully kept and continually put into practice in the various different cultures throughout the course of history. The task of interpreting these prescriptions was entrusted by Jesus to the Apostles and to their successors, with the special assistance of the Spirit of truth: “He who hears you hears me” (Lk 10:16). By the light and the strength of this Spirit the Apostles carried out their mission of preaching the Gospel and of pointing out the “way” of the Lord (cf. Acts 18:25), teaching above all how to follow and imitate Christ: “For to me to live is Christ” (Phil 1:21).
— Veritatis Splendor 25