“The devil is doing his worst against this article of the divinity and the humanity of Christ, which he finds intolerable. Christ must be true God, in accord with the powerful testimony of Scripture and particularly of St. Paul, who declares that in Him the whole fullness of the Deity dwells bodily (Col. 2:9); otherwise we are damned forever. But in His humanity He must also be a true and natural son of the Virgin Mary, from whom He inherited flesh and blood as any other child does from its mother. He was conceived of the Holy Spirit, who came upon her and overshadowed her with the power of the Most High, according to Luke 1:35. However, Mary, the pure virgin*, had to contribute of her seed and of the natural blood that coursed from her heart. From her He derived everything, except sin, that a child naturally and normally receives from its mother. This we must believe if we are not to be lost. If, as the Manichaeans allege, He is not a real and natural man, born of Mary, then He is not of our flesh and blood. Then He has nothing in common with us; then we can derive no comfort from Him” (Luther’s Works, vol. 22, p.22).
Note: Luther did not believe that Mary was without sin, but pure through faith in Christ.