Then Mary said, ‘Here am I, the servant of the Lord; let it be with me according to your word.’  
When I was a young boy I remember my dad telling me, “Don’t ever volunteer for anything.”  Yet isn’t one of the themes of the Word of God, the willingness to volunteer?  When Isaiah was called to be a prophet he didn’t want any part of the job.  He came up with the excuse.  “Not me, I am a man of unclean lips.”   Mary said, “Not me, I am not even married.”  Each of them was asked to make the leap of faith; to put aside their excuses, and let God be God.  God told Isaiah not to worry that He would give Isaiah the words to say.  He told Mary not to worry, that with Him nothing was impossible.  God said, “All you have to do is trust me and I will give you everything you need.”  In the end, they both trusted God and said, “Here am I.”  When God calls you just say, “Here I am,” and trust that God will take care of the rest.