Thomas Aquinas, Compendium of Theology

Valentinus admitted that Christ had a real body. However, he insisted that our Lord did not take flesh from the Blessed Virgin, but rather brought down with Him a body formed of celestial matter. This body passed through the Virgin without receiving anything from her, much as water passes through a canal.

This hypothesis, too, contradicts the truth of Scripture. In Romans 1:3 the Apostle says that God's Son "was made to Him of the seed of David, according to the flesh." And in Galatians 4:4 St. Paul writes: "God sent His Son, made of a woman." Matthew likewise relates: "And Jacob begot Joseph, the husband of Mary, of whom was born Jesus, who is called Christ" (Matt. 1:16). A little later Matthew refers to her as Christ's mother: "When His mother Mary was espoused to Joseph," etc. None of this would be true if Christ had not received His flesh from the Virgin. Accordingly the doctrine that Christ brought with Him a celestial body is false.

True, in I Corinthians 15:47 the Apostle states that "the second man" [Christ, as contrasted with Adam, the first man] was "from heaven, heavenly." But this is to be understood in the sense that He came down from heaven in His divinity, not according to the substance of His body.

Moreover, there would be no reason why the Son of God, bringing His body from heaven, should have entered the Virgin's womb, if He were to receive nothing from her. Such a procedure would seem to be a kind of deceit if, coming forth from His mother's womb, He were to intimate that He had received from her a body which in fact He had not received. Since, therefore, all falsehood is foreign to Christ, we must acknowledge without reservation that He came forth from the Virgin's womb in such a way that He really took His flesh from her.