2 All this is indeed as it is: He, Who is by nature God of God, must possess the nature of His origin, which God possesses, and the indistinguishable unity of a living nature cannot be divided by the birth of a living nature. Yet nevertheless the heretics, under cover of the saving confession of the Gospel faith, are stealing on to the subversion of the truth: for by forcing their own interpretations on words uttered with other meanings and intentions, they are robbing the Son of His natural unity.
Thus to deny the Son of God, they quote the authority of His own words, Why do you call Me good? None is good, save one, God. These words, they say, proclaim the Oneness of God: anything else, therefore, which shares the name of God, cannot possess the nature of God, for God is One. And from His words, This is life eternal, that they should know You the only true God, they attempt to establish the theory that Christ is called God by a mere title, not as being very God.
Further, to exclude Him from the proper nature of the true God, they quote, The Son can do nothing of Himself except that which He has seen the Father do. They use also the text, The Father is greater than I. Finally, when they repeat the words, Of that day and that hour knows no one, neither the angels in heaven, nor the Son, but the Father only, as though they were the absolute renunciation of His claim to divinity, they boast that they have overthrown the faith of the Church.
The birth, they say, cannot raise to equality the nature which the limitation of ignorance degrades. The Father's omniscience and the Son's ignorance reveal unlikeness in the Divinity, for God must be ignorant of nothing, and the ignorant cannot be compared with the omniscient. All these passages they neither understand rationally, nor distinguish as to their occasions, nor apprehend in the light of the Gospel mysteries, nor realize in the strict meaning of the words and so they impugn the divine nature of Christ with crude and insensate rashness, quoting single detached utterances to catch the ears of the unwary, and keeping back either the sequel which explains or the incidents which prompted them, though the meaning of words must be sought in the context before or after them.
Source: On the Trinity (New Advent)