Previously I wrote about the Blessed Mother's perpetual virginity. No one answered my question why is it so important to us that she remained a virgin.
However, if she weren't, then we'd have to change our thinking and opinions and beliefs about Joseph and Mary.
Leila at Little Catholic Bubble explained Mary's virginity. Here's my summary: Joseph knew that Mary was united with the Holy Spirit, and that God was the Father of baby Jesus.
Joseph thought, "Whoa, man! It's like she really IS married to God. I better not mess with Mary! I just better keep my hands to myself and restrict my duties to carrying the heavy pottery and leading the way to Egypt. I don't want to get on God's bad side."
Of course, Joseph helped out Mary in many ways and with the raising of Jesus.