How do those that deny the perpetual virginity of Mary explain the failure of Joseph and Mary to consummate their marriage before the birth of Jesus?
We read in the Gospel of Matthew:
He had no relations with her until she bore a son, and he named him Jesus. (Matthew 1:25)
Matthew gives us a reasonable explanation for Joseph bringing Mary into his home despite her pregnancy:
...the angel of the Lord appeared to him in a dream and said, "Joseph, son of David, do not be afraid to take Mary your wife into your home. For it is through the holy Spirit that this child has been conceived in her. She will bear a son and you are to name him Jesus, because he will save his people from their sins." (Matthew 1:20-21)
However, the angel doesn't say anything about abstaining from the marital act. On the contrary, the direction to "take Mary your wife into your home," heard by a first-century Jew, would seem to imply "take Mary and consummate your marriage."
I expect an answer to include the following verse in the same gospel:
"Behold, the virgin shall be with child and bear a son, and they shall name him Emmanuel," which means "God is with us." (Matthew 1:23)
Did both Joseph and Mary feel obliged to honor Isaiah's prophecy? Did they both know it applied to them? If so, what is the evidence?