One of the old disputes in Christianity is what did the evangelist Matthew mean by the following verse:
Now the birth of Jesus Christ was as follows: After His mother Mary was betrothed to Joseph, before they came together, she was found with child of the Holy Spirit.
Matthew 1: 18
St. Jerome provides the following explanation:
“Therefore, it is not necessary that the things one was planning to do should really happen, should something else intervene to prevent them from happening. Thus, when the evangelist says, “Before they came together”, he means that the time of the wedding is near and that things have reached the point that she who had been considered engaged was about to become a wife.”
Jerome, De perpetua virginitate, s; PL 23, 195-6.
If you are interested in more quotes on Virgin Mary, you can find them in Mary and the Fathers of the Church on Amazon in both in Kindle and paperback formats.
References:
Gambero, L., 1999. Mary and the Fathers of the Church 1st ed. Translated by Buffer, T., San Francisco: Ignatius Press.