One such example is Matthew Here's a traditional response:. There is another passage usually brought up as a evidence that Mary was not perpetually a virgin, Matthew 1. And he called his name Jesus. To say that Joseph "knew her not until she had given birth to a son" my emphasis , many Protestants argue, seems to imply very strongly that Joseph did "know" Mary after she had given birth to Jesus.
Protestant views on Mary
Perpetual Virginity of Mary: Held by All Protestant Reformers | Dave Armstrong
Mary is a touchy subject for Protestants. I get it. Really, I get it. The majority of my life I sat in the pews of a very conservative Protestant Church with very Protestant views of Mary. At that time, I had the utmost confidence that I was right about Mary; but I had also devoted strikingly little study to the subject. So how did I know that what I believed about her was the truth? The Protestant hesitancy to accept what the Roman Catholic and Orthodox Churches teach about Mary comes from a good place: the concern to safeguard a proper teaching about Christ and to keep him at the center of Christianity.
The Bible allows for it
Once upon a time, almost no Christians denied that Mary the mother of Jesus was perpetually a virgin: including Protestants. Of the early leaders of that movement, virtually all fully accepted this doctrine: including Luther, Calvin, Zwingli, Bullinger, Turretin, and Cranmer. But today, for various reasons, things are very different, so it's helpful to revisit the biblical arguments, since the Bible is the authority all Christians revere in common.
I firmly believe that Mary, according to the words of the Gospel as a pure Virgin, brought forth for us the Son of God, and in childbirth and after childbirth forever remained a pure, intact Virgin. Luther defended the dogma after being excommunicated. Calvin is more difficult to pin down.