What can I give Him, poor as I am?
If I were a shepherd, I would bring a lamb;
If I were a Wise Man, I would do my part;
Yet what I can I give Him: give my heart.
The purpose of advent is to prepare one's heart - to purify it - so as to make it a fitting place for Christ to be born. At Christmas we give Him our heart, as the wise men gave their gifts and the shepherd's their lambs.