Calvin on Perpetual Virginity of Mary
While most Protestants reject perpetual virginity of Mary, it was not the position adopted by one of Reformers, John Calvin. In his commentary on Harmony of the Evangelists Matthew, Mark and Luke he wrote on Matthew 1:25
And knew her not This passage afforded the pretext for great disturbances, which were introduced into the Church, at a former period, by Helvidius [c. 4th century AD]. The inference he 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. Jerome [c. 347 to 420 AD], on the other hand, earnestly and copiously defended Mary’s perpetual virginity. Let us rest satisfied with this, that no just and well-grounded inference can be drawn from these words of the Evangelist, 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. It is said that Joseph knew her not till she had brought forth her first-born son: but this is limited to that very time. What took place afterwards, the historian does not inform us. Such is well known to have been the practice of the inspired writers. Certainly, no man will ever raise a question on this subject, except from curiosity; and no man will obstinately keep up the argument, except from an extreme fondness for disputation.
John Calvin, Commentary on a Harmony of the Evangelists, Matthew, Mark and Luke, First Volume (page 107)
Calvin understood that brothers of Christ were his relatives (cousins) and this is in line with what Catholics believe.
The word brothers, we have formerly mentioned, is employed, agreeably to the Hebrew idiom, to denote any relatives whatever; and, accordingly, Helvidius displayed excessive ignorance in concluding that Mary must have had many sons, because Christ’s brothers are sometimes mentioned.
John Calvin, Commentary on a Harmony of the Evangelists, Matthew, Mark and Luke, Second Volume (page 215)
Luke VIII.19. And his mother and his brethren came to him. There is an apparent discrepancy here between Luke and the other two Evangelists; for, according to their arrangement of narrative, they represent Christ’s mother and cousins as having come.
John Calvin, Commentary on a Harmony of the Evangelists, Matthew, Mark and Luke, Second Volume (page 89)
English translation is taken from Calvin’s Commentaries, Vol. 16, translated by Rev. William Pringle, published by Baker Book House, Grand Rapid Michigan. All Calvin’s Commentaries are available online at http://www.ccel.org/.