I don’t think it’s so clear because both Luther and Calvin upheld the perpetual virginity of Mary and the perspicuity of Scripture:
All of the early Protestant Founders accepted the truth of the Perpetual Virginity of Mary. How could this be, if it is merely “tradition” with no scriptural basis? Why was its supposed violation of Scripture not so obvious to them, as it is to the Protestants of the last 150 years or so (since the onset of theological liberalism) who have ditched this previously-held opinion?
Luther and Calvin on Perpetual Virginity of Mary
Luther:
Christ . . . was the only Son of Mary, and the Virgin Mary bore no children besides Him . . . I am inclined to agree with those who declare that ‘brothers’ really mean ‘cousins’ here, for Holy Writ and the Jews always call cousins brothers.
When Matthew [1:25] says that Joseph did not know Mary carnally until she had brought forth her son, it does not follow that he knew her subsequently; on the contrary, it means that he never did know her . . . This babble . . . is without justification . . . he has neither noticed nor paid any attention to either Scripture or the common idiom.
Editor Jaroslav Pelikan (Lutheran) adds:
Luther . . . does not even consider the possibility that Mary might have had other children than Jesus. This is consistent with his lifelong acceptance of the idea of the perpetual virginity of Mary.
Calvin:
Helvidius displayed excessive ignorance in concluding that Mary must have had many sons, because Christ’s ‘brothers’ are sometimes mentioned.
[On Matt 1:25:] The inference he [Helvidius] drew from it was, that Mary remained a virgin no longer than till her first birth, and that afterwards she had other children by her husband . . . No just and well-grounded inference can be drawn from these words . . . as to what took place after the birth of Christ. He is called ‘first-born’; but it is for the sole purpose of informing us that he was born of a virgin . . . What took place afterwards the historian does not inform us . . . No man will obstinately keep up the argument, except from an extreme fondness for disputation.
Zwingli:
I have never thought, still less taught, or declared publicly, anything concerning the subject of the ever Virgin Mary, Mother of our salvation, which could be considered dishonourable, impious, unworthy or evil . . . I believe with all my heart according to the word of holy gospel that this pure virgin bore for us the Son of God and that she remained, in the birth and after it, a pure and unsullied virgin, for eternity.
John Wesley:
I believe… he [Jesus Christ] was born of the blessed Virgin, who, as well after as she brought him forth, continued a pure and unspotted virgin.
This brought to you by Shellie…. I just wanted to have it handy for the next time it comes up.