God is the First and Last, serving as the beginning and end of all things (CCC 198), God’s eternity is infinite and unchanging. This distinction emphasizes His transcendence and His status as the only uncreated being. (CCC 213)

This eternity is shared within the Blessed Trinity. The Word of God is coeternal with God, acting as the Beginning through whom heaven and earth were created (CCC 241-242). Similarly, the Holy Spirit proceeds eternally from both the Father and the Son, a fact that affirms their consubstantial communion (CCC 243-245).

Because God is eternal, His knowledge is not limited by the constraints of time or space. He knows all things past and future without any distraction or change in His understanding (CCC 600, Psalm 139:4). Furthermore, God is Truth, and His everlasting love is victorious over all infidelities (Ps 119:160, CCC 215, Jn 3:16).

God extends the promise of eternity to humanity through the gift of eternal life. Jesus Christ is the source of this life, and those who believe in Him will receive it (Jn 6:47, CCC 1020). This gift is initiated through the sacrament of Baptism, which seals the faithful for eternal life (CCC 1272), and is nourished by the Eucharist, which serves as the seed of eternal life and is necessary for spiritual nourishment (Jn 6:53-54, CCC 1322-1335).

Eternal life is a gratuitous gift of mercy made possible by supernatural grace (CCC 1727). The ultimate goal of this life is the beatitude of God, where creatures enter into the perfect unity of the Blessed Trinity (CCC 260) and God becomes all in all, pouring out His gifts through the Son and Holy Spirit (1 Cor 15:28).

The transition to this eternal state occurs at death, which is not an end but a passage to eternal life (CCC 1012-1013). At the moment of death, each person undergoes a Particular Judgment to receive their eternal retribution in their immortal soul (CCC 1022, 1051). This results in either an everlasting dwelling place in heaven (CCC 1012) or a state of eternal separation from God in hell (CCC 1057). Ultimately, the Kingdom of God will reach its fullness, and the righteous will be raised with incorruptible and immortal bodies to reign with Christ forever (1 Cor 15:50-52, CCC 1042).