The Jewish nation achieved a unique relationship when they accepted the responsibilities of the Torah. Performing all of the mitzvos. HaShem promised Moshe that by our acceptance of the Torah, even if we do not fulfill its mitzvos we will always be His special treasure from among the nations. However, if we diligently fulfill all that the Torah commands us we will become even more endeared to Him, having made ourselves into a Holy nation. The Torah even demands that we must not desire that which is not ours.
Desires often assail a person involuntarily.
Imagine a person with a craving for a forbidden food that he saw on the other side of a frozen river. His mouth watering, he races across the ice. If he would suddenly slip, he would immediately forget all about his desires. A person's nature is such that even a relatively little fear removes all of his desires and lusts. Therefore, since the Torah has warned us to avoid these lusts, if we would now only have a little fear of transgression we could avoid these desires.