When a large amount of ashes accumulated on the altar, as a remnant of the many slaughtered animals, a priest would collect the ashes and bring them outside of the camp. When he brought the ashes outside, he changed out of his priestly garments into other, simpler ones.

Rashi explains in his commentary, "A servant would not wear the same garments to cook a meal for his master as he does to serve him." The work that the priest did within the Temple, where the Divine Presence rests, was considered "serving his master," and thus he did them wearing the priestly garments. When going outside of the Temple, though, where the Divine Presence does not dwell, the priest changed out of usual his garments.

This teaches us a lesson for life. Everyone has a unique task to perform in life. Some of us work in jobs that are considered more distinguished and respectable, and dress accordingly. However, we sometimes need to go outside our comfort zone in order to help others. This might require getting dirty, either literally or metaphorically.

When we demonstrate our readiness to change out of our regular clothing and get dirty for the sake of someone else, G-d will reciprocate in kind. He will descend into the darkness of this world in order to elevate and purify us.

(Likutei Sichos, Volume 37, p. 1)