One teaching of the Catholic Church that Protestants generally reject is the teaching that Mary remained a virgin through her entire life.
They will typically point to Mark 6:3, which mentions "brothers and sisters" of Jesus, as if Catholics were simply unaware of this verse!
To be clear, the term in the original language can mean cousins and this was always the understanding of the Church.
Here is a longer answer about those Bible verses-
But actually, with those verses out of the way, because they can mean cousins, we can move on to actually PROVE that the BIBLE shows Mary was ever virgin!
First of all, we must prove she was the ARK of the NEW COVENANT, holding the WORD OF GOD (the Word made flesh for the New Covenant). I showed this in a prior article-
Next, we must show what happened to people who touched the ARK OF THE COVENANT-
(1 Samuel 6)
"The great stone, beside which they set down the ark of the Lord, is a witness to this day in the field of Joshua of Beth-she′mesh.
19 And he slew some of the men of Beth-she′mesh, because they looked into the ark of the Lord; he slew seventy men of them, and the people mourned because the Lord had made a great slaughter among the people.
(2 Samuel 6)
6 And when they came to the threshing floor of Nacon, Uzzah put out his hand to the ark of God and took hold of it, for the oxen stumbled. 7 And the anger of the Lord was kindled against Uzzah; and God smote him there because he put forth his hand to the ark; and he died there beside the ark of God.
NO ONE can touch the ARK! That would include St. Joseph. He certainly did not enter into the ARK and Mary remained EVER VIRGIN.
This is a BIBLICAL teaching that Protestants don't know about. Tell them so they can learn about the BIBLE they love!