But the truth is, we find that He is expressly set forth as both God and Man; the very psalm which we have quoted intimating (of the flesh), that “God became Man in the midst of it, He therefore established it by the will of the Father,”—certainly in all respects as the Son of God and the Son of Man, being God and Man, differing no doubt according to each substance in its own especial property, inasmuch as the Word is nothing else but God, and the flesh nothing else but Man. Thus does the apostle also teach respecting His two substances, saying, “who was made of the seed of David;” in which words He will be Man and Son of Man. “Who was declared to be the Son of God, according to the Spirit;” in which words He will be God, and the Word—the Son of God. We see plainly the twofold state, which is not confounded, but conjoined in One Person—Jesus, God and Man.
…In like manner, again, the apostle calls Him “the Mediator between God and Men,” and so affirmed His participation of both substances.
Tertullian
Against Praxeas
Chapter XXVII