4 In this distorted and depraved rule of his own heart, let the heretic hear us, not as yet chiding, but still as it were inquiring, and let him explain to us what he thinks. For, I suppose, whoever you are (for we may regard him as here present in person), you hold with us, that “in the beginning was the Word.” I do hold it, says he. And that “the Word was with God”? This too, says he, I hold. Proceed then, and hold the stronger saying that follows, that “the Word was God.”
Even this, says he, I hold: but yet, this, God the greater; that, God the less. Now this somehow smells of the pagan: I thought I was speaking with a Christian. If there is God the greater, and God the less, then we worship two Gods, not one God. Why, says he; do not you, too, affirm two Gods, equal the one to the other? This I do not assert: for I understand this equality as implying therein also undivided love; and if undivided love, then perfect unity. For if the love that God put in men does make of many hearts of men one heart, and does make many souls of men into one soul, as it is written of them that believed and mutually loved one another, in the Acts of the Apostles, “They had one soul and one heart toward God:” if, therefore, my soul and your soul become one soul, when we think the same thing and love one another, how much more must God the Father and God the Son be one God in the fountain of love!
Source: Tractates on the Gospel of John (New Advent)