From Pope St. John Paul II’s encyclical Veritatis Splendor (1993):
The Church, instructed by the Teacher’s words, believes that man, made in the image of the Creator, redeemed by the Blood of Christ and made holy by the presence of the Holy Spirit, has as the ultimate purpose of his life to live “for the praise of God’s glory” (cf. Eph 1:12), striving to make each of his actions reflect the splendour of that glory. “Know, then, O beautiful soul, that you are the image of God”, writes Saint Ambrose. “Know that you are the glory of God (1 Cor 11:7). Hear how you are his glory. The Prophet says: Your knowledge has become too wonderful for me (cf. Ps. 138:6, Vulg.). That is to say, in my work your majesty has become more wonderful; in the counsels of men your wisdom is exalted. When I consider myself, such as I am known to you in my secret thoughts and deepest emotions, the mysteries of your knowledge are disclosed to me. Know then, O man, your greatness, and be vigilant”.17
What man is and what he must do becomes clear as soon as God reveals himself. The Decalogue is based on these words: “I am the Lord your God, who brought you out of the land of Egypt, out of the house of bondage” (Ex 20:2-3). In the “ten words” of the Covenant with Israel, and in the whole Law, God makes himself known and acknowledged as the One who “alone is good”; the One who despite man’s sin remains the “model” for moral action, in accordance with his command, “You shall be holy; for I the Lord your God am holy” (Lev 19:2); as the One who, faithful to his love for man, gives him his Law (cf. Ex 19:9-24 and 20:18-21) in order to restore man’s original and peaceful harmony with the Creator and with all creation, and, what is more, to draw him into his divine love: “I will walk among you, and will be your God, and you shall be my people” (Lev 26:12).
The moral life presents itself as the response due to the many gratuitous initiatives taken by God out of love for man. It is a response of love, according to the statement made in Deuteronomy about the fundamental commandment: “Hear, O Israel: The Lord our God is one Lord; and you shall love the Lord your God with all your heart, and with all your soul, and with all your might. And these words which I command you this day shall be upon your heart; and you shall teach them diligently to your children” (Dt 6:4-7). Thus the moral life, caught up in the gratuitousness of God’s love, is called to reflect his glory: “For the one who loves God it is enough to be pleasing to the One whom he loves: for no greater reward should be sought than that love itself; charity in fact is of God in such a way that God himself is charity”.18
17 Exameron, Dies VI, Sermo IX, 8, 50: Corpus Scriptorum Ecclesiasticorum Latinorum 32, 24.
18 Saint Leo the Great, Sermo XCII, Chap. III: Patrologia Latina 54, 454.
— Veritatis Splendor 10