Heretics, among their other impieties, misinterpret these words of our Lord’s, and say, that if His Father is their Father, His God their God, He cannot be God Himself. But though He remained in the form of God, He took upon Him the form of a servant; and Christ says this in the form of a servant to men. And we cannot doubt that in so far as He is man, the Father is His Father in the same sense in which He is of other men, and God His God in like manner. Indeed He begins with saying, Go to My brethren. But God can only have brethren according to the flesh; the Only-Begotten God, being Only-Begotten, is without brethren.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: de Trin.