Beliefs Lead to Desires?

After our last class, I was a little confused as to why beliefs lead to desires. I always though that you can believe in something like morality without desire. For example, i could do something good for someone without looking for anything in return. In other words, by committing myself to selfless action, I would not have any desire. However, I did not realize that my belief in selflessness created a desire to act selflessly. In performing action there is still motive or desire. Likewise non-human animals performing actions do so with desire no matter how minute the impulse that drives seems.