Gospel Guidebook: Getting and Keeping It Right 
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When Did "One God the Father" Become the "Triune God"?
by Robert P. TerryUpdated May 18, 2026
Philip Schaff in his book "Creeds of Christendom, Volume II" provides a Comparative Table of the Ante-Nicene Rules of Faith on page 40 (available here) that shows that the one true God up until the end of the fourth century was unanimously the Father. At some point in time, however, the church apostatized from this rule of faith and replaced God the Father with the Triune God. Knowing how jealous God is for His name, this ought to send shivers down our spines. How could this have happened? Even in our day, it is nearly impossible to read a theology book (especially one written by a Reformed theologian) and not constantly see God referred to as "our Triune God."
It appears that the initial culprit behind this perversion of the rule of faith was Augustine of Hippo. He wrote 15 volumes on the Trinity and referred to God as the Trinity, prayed to God as the Trinity, and worshiped God as the Trinity. And because of his popularity and influence, the whole Christian church (at least in the West) became infected by his poison. Here are just a few examples of Augustine referring to God as the Trinity:
In Book 2, Chapter 10 speaking of Abraham he says, "...neither here does it appear plainly whether it was any person of the Trinity that appeared to Abraham, or God Himself the Trinity, of which one God it is said, You shall fear the Lord your God, and Him only shall you serve." Augustine quotes Deuteronomy 6:13, which is in the same context of the Shema, and refers to the Lord God as the Trinity, even going to so far as to use the singular personal pronoun "himself." In other words, for Augustine the Trinity is not only God, but also a person (which would actually give us four persons, the Father, Son, Holy Spirit, and Trinity).
In Book 15, Chapter 28, Augustine goes so far as to pray to the Trinity, saying "O Lord our God, we believe in You, the Father and the Son and the Holy Spirit. For the Truth would not say, Go, baptize all nations in the name of the Father and of the Son and of the Holy Spirit, unless You were a Trinity. Nor would you, O Lord God, bid us to be baptized in the name of Him who is not the Lord God. Nor would the divine voice have said, Hear, O Israel, the Lord your God is one God, unless You were so a Trinity as to be one Lord God...O Lord the one God, God the Trinity, whatever I have said in these books that is of Yours, may they acknowledge who are Yours; if anything of my own, may it be pardoned both by You and by those who are Yours. Amen."
Finally, as one more example from Section 11 in his debate with Maximinus (the Arian), Augustine speaks of worshiping the Trinity and actually quotes the Shema. "Hence, we worship the Trinity, because the Father is not the Son and the Son is not the Father and the Holy Spirit is neither the Father nor the Son, but we still worship one God, because the ineffable and lofty union of the Trinity reveals that there is one God, one Lord. Thus scripture said, Hear, O Israel, the Lord is your God, the Lord is one (Dt 6:4)."