The formation of the Trinitarian dogma
250 From the beginning, the revealed truth of the Holy Trinity has been at the very root of the Church’s living faith, principally by means of Baptism. It finds its expression in the rule of baptismal faith, formulated in the preaching, catechesis and prayer of the Church. Such formulations are already found in the apostolic writings, such as this salutation taken up in the Eucharistic liturgy: “The grace of the Lord Jesus Christ and the love of God and the fellowship of the Holy Spirit be with you all.” 81
251 In order to articulate the dogma of the Trinity, the Church had to develop her own terminology with the help of certain notions of philosophical origin: “substance”, “person” or “hypostasis”, “relation” and so on. In doing this, she did not submit the faith to human wisdom, but gave a new and unprecedented meaning to these terms, which from then on would be used to signify an ineffable mystery, “infinitely beyond all that we can humanly understand”. 82
81 2 Cor 13:14; cf. 1 Cor 12:4-6; Eph 4:4-6.
82 Paul VI, CPG § 2 [CPG = Solemn Profession of faith : Credo of the People of God]