8 I felt that I must spare a little space to point this out. It has been from no love for amplification, but that it might serve as a warning. First, I wished to expose the vague and confused character of this crowd of heresies, whose mutual feuds turn, as we have seen, to our advantage. Secondly, in my warfare against the blasphemous doctrines of modern heresy; that is, in my task of proclaiming that both God the Father and God the Son are God—in other words, that Father and Son are One in name, One in nature, One in the kind of Divinity which they possess—I wished to shield myself from any charge which might be brought against me, either as an advocate of two Gods or of one lonely and isolated Deity.
For in God the Father and God the Son, as I have set them forth, no confusion of Persons can be detected; nor in my exposition of Their common nature can any difference between the Godhead of the One and of the Other be discerned. In the preceding book I have sufficiently refuted, by the witness of the Gospels, those who deny the subsistence of God the Son by a true birth from God; my present duty is to show that He, Who in the truth of His nature is Son of God, is also in the truth of His nature God. But this proof must not degenerate into the fatal profession of a solitary God, or of a second God. It shall manifest God as One yet not alone; but in its care to avoid the error of making Him lonely it shall not fall into the error of denying His unity.
Source: On the Trinity (New Advent)