The strongest urge of man is his sexual urge. It is overwhelming for many. The age old question for those who want to remain holy is ... HOW?? How can one control his thoughts, feelings, desires and behavior??
We cannot live in a vacuum. Just saying "don't think about it" won't work. There must be a substitute desire that is so powerful that it overpowers even the sexual urge. What can that be?
The desire to be close to Hashem. THAT is the avodah. If one is passionate enough about Hashem then he can keep his sexual urges at bay.
See here.
