In order, therefore, that He who was already the Son of God—of God the Father’s seed, that is to say, the Spirit—might also be the Son of man, He only wanted to assume flesh, of the flesh of man without the seed of a man; for the seed of a man was unnecessary for One who had the seed of God. As, then, before His birth of the virgin, He was able to have God for His Father without a human mother, so likewise, after He was born of the virgin, He was able to have a woman for His mother without a human father. He is thus man with God, in short, since He is man’s flesh with God’s Spirit—flesh (I say) without seed from man, Spirit with seed from God. For as much, then, as the dispensation of God’s purpose concerning His Son required that He should be born of a virgin, why should He not have received of the virgin the body which He bore from the virgin?
Tertullian
On the Flesh of Christ
Chapter XVIII