In Irenaeus’ great studyDemonstration of the Apostolic Preaching we are treated in paragraph six to one of the earliest summaries of the principle articles of the Christian faith. Here they are:
Is there any story of the Christian faith that can ignore these three articles? Trinitarian faith is the historic faith of the Church. Already in the 2d Century — not fourth — Irenaeus not only teaches a Trinity-shaped faith but assumes this is the only faith the Church knows.
Second, “the Word of God, the Son of God, Christ Jesus our Lord … revealed by the prophets … “by whom all things were made” and “who, in the last times, to recapitulate all things, became a man amongst men, visible and palpable, in order to abolish death, to demonstrate life, and to effect communion between God and man.
Third, the Holy Spirit. What here? It was through the Spirit the prophets did their work, it was through the Spirit that the patriarchs learned, it was through the Spirit that the righteous were led, and who was poured out “in a new fashion upon the human race renewing man, throughout the world, to God” .