Queen of Israel
Recently, a friend asked a very interesting question. Why do Catholics (and Orthodox) refer to Mary as a queen? The answer is that, even on Protestant terms of Sola Scriptura, she is one.
In the Kingdom of Israel, there was always one queen, but the kings often had more than one wife. How did this work? For the simple reason that in Israel, the queen wasn't the king's wife, but the king's mother. This can be seen in the relationship between Solomon and Bathsheba, for instance.
So, if the queen of Israel is always the mother of the king, what happens when Jesus is the Heir of David, and King of Israel? By the laws and customs of Israel, Jesus's mother is the queen of Israel, even if she wasn't a descendant of David herself.
Lest it be thought that this threatens the royal prerogatives of Christ, it is worth noting that the queens of Israel had no power in their own right, but only by virtue of their relationship to the son. If the king were to for some reason become displeased with the queen, she had no legal or customary authority by which she could resist him, and as soon as the king died and the kingship passed to another, she was no longer the queen.
Queen of Heaven
All right, you might say, but surely Mary's title as Queen of Heaven is going too far?
If you read Revelation 12, you'll find a mysterious figure: a woman clothed with the sun, standing on the moon, with a crown of 12 stars on her head. The 12 stars indicate the 12 tribes of Israel, or the 12 apostles. What is significant is that a little bit later, we discover that this woman is pursued by a dragon and she gives birth to a son who will "rule the nations." This son is obviously Christ. So Christ's mother is shown in a symbolic way to be a queen, and more specifically, a queen of heaven.
How can this be?
Well, consider how the book of Revelation ends. It ends with the descent of the new Jerusalem, which is obviously meant to symbolize in some way the descent of Heaven to Earth. And Mary, as we saw earlier, is the mother of the King of the New Jerusalem. So it is in that sense that Mary is queen of heaven: not in her own right, but by the grace of her son. She is the icon and greatest example of what we all shall be, kings and queens reigning with Christ our King.