When the angel said, "Let me go, for the dawn has risen", Jacob responded by saying "Are you a thief or a gambler who is afraid of the dawn?" The angel replied, "I am an angel and from the day that I was created my time to recite a song before G-d had not arrived until now". The Gemara asks why at this point in battle the angel chooses to praise G-d.
The rabbis teach us that all of creation, including angels, can sing praises to G-d but only when it serves its purpose of being created. When this is expanded to the Jewish People as a whole, We reached our highest level when we crossed the Red Sea after the exodus from Egypt. We sang Az Yashir (Shemot, ch.15) at that very moment.
The rabbis suggest that the angel is the spiritual representation of Esau, Jacob's older brother who wrongly lost his birthright after their mother was told of her sons that "the elder shall serve the younger" (Bereishit 25:23). The rabbis teach us that in the exact moment that the angel lost his battle to Jacob, he reached his purpose in creation - to help with Jacob's spiritual development. They reaffirm that only in a moment of defeat can we sing praises to G-d.