The Torah tells us that Yaakov was attacked by the Malach of Esav. As dawn approached and Yaakov prevailed, the malach asked to be freed. Chazal tell us that the reason it was so urgent for the Malach to leave, was because each Malach receives one chance to say Shira and precisely on that day the turn of the Malach of Esav had arrived.
Rav Dessler ZT”L points out that obviously the remarkable “coincidence” of these two occurrences was not by chance. He explains that the opportunity of a Malach to say Shira arises when he has completed the mission for which he was created. The mission of the Malach of Esav was completed after he fought with Yaakov AND YAAKOV WON!
What a paradox! Although the task of the Yetzer Hara is to fight with each one of us mercilessly, his achievements are measured by OUR SUCCESS in beating him.