Early Christian Confession
Augustine explained the Trinity like this:
[T]he Father, and the Son, and the Holy Spirit intimate a divine unity of one and the same substance in an indivisible equality; and therefore that they are not three Gods, but one God: although the Father hath begotten the Son, and so He who is the Father is not the Son; and the Son is begotten by the Father, and so He who is the Son is not the Father; and the Holy Spirit is neither the Father nor the Son, but only the Spirit of the Father and of the Son, Himself also co-equal with the Father and the Son, and pertaining to the unity of the Trinity. … [A]lthough the Father, and the Son, and the Holy Spirit, as they are indivisible, so work indivisibly. This is also my faith, since it is the Catholic faith.
Augustine’s confession here mirrors what the early Church was already confessing, both through the canon and in the creeds. Within the NT text and as early as the first half of the second century, Christians have assigned praise to the persons of the Trinity, not merely to a generic “God.” While infantile in its expression, Christians began moving toward an incipient Trinitarian understanding of the one God of Israel at an early stage. For example, benedictions, doxologies, and venerations are self-consciously attributed to all or some of the divine persons in a score of NT texts (Acts 7:59; Rom. 16:27; 1 Cor. 16:22; 2 Cor. 13:14; Eph. 5:20; Phil. 2:5-11; 2 Pet. 3:1; et al.). The Gospel tradition itself helps lay a solid foundation for understanding the roles and functions of the divine persons that is described in the above-referenced NT literature, with Jesus’s own words and actions showing a self-identification with God (Matt. 9:1-8; Mark 2:28; John 5:16-23, 8:58; et al.). The Trinity is, then, a hermeneutical and devotional effect of reading Scripture in its canonical form and catholic location.