God sits outside of time in addition to being inside of time (He is both transcendent – outside of time, and immanent – inside of time).
God sees things in the ‘Now’ – all creation is available to Him as a ‘Now’ moment.
When He chose a ‘Virgin’ to bear His only Son, the Virgin, when born, now lives inside of time and soon will live outside of time.
To be the God-Bearer, the person (Mary) needed to be sinless, as God does not allow sin to be within contact of His abode. The person of Mary needed to be above the carnal, therefore a Virgin, and to render a miraculous – Virgin – birth.
Mary’s Virginity, when viewed by God outside of time, is of a ‘Now’ or permanent, complete, whole-of-existence person. When living inside of time as a Virgin, she maintains her Virginity outside of time.
If at some point she is not a Virgin inside of time, then outside of time she would also become a non-Virgin which gives rise to a contradiction – the Virgin God-bearer of Jesus would be both a Virgin and non-Virgin.
Mary remains the Mother of Jesus for all times. Jesus is born of a Virgin, so Mary remains a Virgin for all times. Remember, God’s creation and interface with us is a continual act as God does not have a past and future, only a present.
Jesus’ birth and entry into the immanence of time – the Incarnation – is a continuing act since, as God, He does not have a past and future (“before Abraham was, I am”) only a present. Jesus’ past and future are only applicable to His humanity. Since the Incarnation is a continuing event, then Mary’s Virginity and freedom from sin must remain continuous and not changing.
Remember too, that when the ancient Israelites refereed to a woman as a Virgin, they meant fully and completely throughout the woman’s life. Today, our dual meaning of Virgin includes a woman who has not had sexual intercourse as yet. This is not the meaning of Virgin in the Bible.
In the Bible translations the Aorist tense is often used. This tense indicates perfection and does not determine any completion. Aorist is used in continuing situations where the writer simply wrote the inspired word of God. The Bible translations we now use may not reflect the original writer’s ideas.
When Matthew wrote about Mary’s Virgin birth, he wrote in the genre of the time which was up to the point he knew, and had no reference to future events.
A way to understand the concept of time for the Hebrews and Greeks of that era is: Picture yourself sitting on a train, but sitting backwards in the caboose. You can see the scenery that just passed by, but nothing moving ahead. This is the way people of those generations used to view the future – as they did not know the future, they simply wrote about what they had seen.