From my reading in Luke 1:21-38 in the One Year New Testament.
Why Mary?
Mary just got done hearing what would be the most life changing news of her life! The angel Gabriel just finish telling her she would have a son by the Holy Spirit and this was her response.
“I am the Lord’s servant. May everything you have said about me come true.” Luke 1:38
I believe this attitude is one of the reasons God chose Mary for this noble task. She was a servant. Mary was humble and willing to accept whatever God had for her. This allowed her to trust God even for the most miraculous of events.
Mary is a great example of humble service of God. If you want to be used by God in powerful ways you must be willing to accept whatever the Lord brings you.
Are you open to God using you, even to do something unusual?