The mystery of the one God: Father, Son and Holy Spirit
The history of salvation is the story of how the one, true God, Father, Son and Holy Spirit, revealed himself to the human race, reconciled and joined to himself those who had turned away from their sins.
The Old Testament, while clearly affirming the unity of God in a polytheistic world, already foreshadows to some extent the mystery of the Trinity, which is fully unfolded in the person and in the words of Jesus Christ. For when he reveals himself as Son of God, he also reveals the Father and the Holy Spirit. An intimate knowledge of the true God pervades the entire soul of the divine Master. He communicates it to his followers, inviting them to become sons of God through the gift of his filial Spirit which he bestowed on them (see John 1:12).
In catechesis therefore the encounter with God one and triune occurs first and principally when the Father, Son and Holy Spirit are recognised as the authors of that plan of salvation which culminated in the death and resurrection of Jesus. In this way, the revelation of the mystery transmitted in the Church is met by the growing awareness of the faithful that from baptism their lives consist in achieving more intimate familiarity with the three divine persons, called as they are to share their divine nature. Lastly, Christians are able, with the eyes of faith, through the gift of the Holy Spirit, to contemplate now and to approach in filial love the most holy Trinity of Persons, as it exists from eternity in God’s intimate life.