8 As we are answering all, even their most insensate statements, we come now to the discussion of the unknown hour. Now, even if, as they say, the Son had not known it, this could give no ground for an attack upon His Godhead as the Only-begotten. It was not in the nature of things that His birth should avail to put His beginning back, until it was equivalent to the existence which is unbegotten, and had no beginning; and the Father reserves as His prerogative, to demonstrate His authority as the Unbegotten, the fixing of this still undetermined day.
Nor may we conclude that in His Person there is any defect in that nature which contained by right of birth all the fullness of that nature which a perfect birth could impart. Nor again could the ignorance of day and hour be imputed in the Only-begotten God to a lower degree of Divinity. It is to demonstrate against the Sabellian heretics that the Father's authority is without birth or beginning, that this prerogative of unbegotten authority is not granted to the Son. But if, as we have maintained, when He said that He knew not the day, He kept silence not from ignorance, but in accordance with the Divine Plan, all occasion for irreverent declarations must be removed, and the blasphemous teachings of heresy thwarted, that the truth of the Gospel may be illustrated by the very words which seem to obscure it.
Source: On the Trinity (New Advent)