Tertullian, early church father of the late 2nd and early 3rd centuries, helped define and defend the doctrine of the Trinity over and against the alternate teachings of some. Some were teaching that God was only one divine being, and any mention of Father, Son or Spirit was simply another way of describing this single being. Tertullian, far from denying the divine oneness, affirmed the status of the Father, Son and Spirit as three separate persons within the unified Godhead. This understanding of God was proclaimed throughout the apostolic churches through the affirmation of the “rule of faith” or basic biblical affirmation of God’s triunity. Heretics, interpreting a few verses to the neglect of the whole, were guilty of presenting a false God. Tertullian states:
In this principle [the rule of faith] also we must henceforth find a presumption of equal force against all heresies whatsoever—that whatever is first is true, whereas that is spurious which is later in date. But keeping this prescriptive rule inviolate, still some opportunity must be given for reviewing (the statements of heretics), with a view to the instruction and protection of divers persons; were it only that it may not seem that each perversion of the truth is condemned without examination, and simply pre- judged; especially in the case of this heresy, which supposes itself to possess the pure truth, in thinking that one cannot believe in One Only God in any other way than by saying that the Father, the Son, and the Holy Ghost are the very selfsame Person. As if in this way also one were not All, in that All are of One, by unity (that is) of substance; while the mystery of the dispensation is still guarded, which distributes the Unity into a Trinity, placing in their order the three Persons—the Father, the Son, and the Holy Ghost: three, however, not in condition, but in degree; not in substance, but in form; not in power, but in aspect; yet of one substance, and of one condition, and of one power, inasmuch as He is one God, from whom these degrees and forms and aspects are reckoned, under the name of the Father, and of the Son, and of the Holy Ghost. – Against Praxeas, 2 (ANF 3:598).
Holding to the confession of faith, passed on from the apostles through the witness of Scripture, is vital in confirming the true faith and proper belief in the one true God. Any picture of God which neglects the threeness presents a false god foreign to the witness of Scripture.