My Soul Magnifies the Lord

What is it that causes us to sing? It is a question I asked myself whilst preparing for Sunday. I am sure there are many answers but a couple would be: a sense of goodwill or happiness; an event that brings great joy; or we are simply caught up by a good tune. Singing, I believe is good for us.
But what causes us to sing from the depths of our being, from the heart? Mary's song, together with those of Zechariah (prophecy) and Simeon in Luke chapter two highlight the majesty, power, saving grace and the mercy of God - all of which fill our own hearts with songs of praise and thanksgiving.