The word "work" is an abstract noun that can be expressed with the verb "serving." Alternate translation: "when serving at the altar" (See: [[rc://en/ta/man/translate/figs-abstractnouns]])
The poles were inserted into rings on the sides of the altar so they could be used to carry it. This can be stated clearly. Alternate translation: "insert the carrying poles into the rings on the sides of the altar" (See: [[rc://en/ta/man/translate/figs-explicit]])