CATECHISM OF THE CATHOLIC CHURCH
The Word became flesh to make us "partakers of the divine nature"(2Pet 1:4): "For this is why the Word became man, and the Son of God became the Son of man: so that man, by entering into communion with the Word and thus receiving divine sonship, might become a son of God (Irenaeus)…"The onlybegotten Son of God, wanting to make us sharers in his divinity, assumed our nature, so that he, made man, might make men gods" (Athanasius).
654. Justification…brings about filial adoption so that men become Christ's brethren…We are brethren not by nature, but by the gift of grace, because that adoptive filiation gains us a real share in the life of the only Son, which was fully revealed in his Resurrection.
1996. Our justification come from the grace of God. Grace is favor, the free and undeserved help that God gives us to respond to his call to become children of God, adoptive sons, partakers of the divine nature and of eternal life.
2009. Filial adoption, in making us partakers by grace in the divine nature, can bestow true merit on us as a result of God's gratuitous justice. This is our right by grace, the full right of love, making us "coheirs" with Christ and worthy of obtaining "the promised inheritance of eternal life" (Council of Trent). The merits of our good works are gifts of the divine goodness. "Grace has gone before us; now we are given what is due…Our merits are God's gifts" (Augustine).