Leviticus 10:6 "Neither rend your clothes"

The priests are given magnificent clothing which they must wear while serving in the Beit HaMikdash.

The Torah describes these clothes and explains in detail how they are designed and sewn (See positive Mitzvah 33).

The priests must be careful that their clothes are well kept and elegant as befitting their work in the Beit HaMikdash.

They are forbidden to enter the Beit HaMikdash if their clothes are torn and shabby.

In addition, the act of rending (tearing) one's clothes is a symbol of mourning.

When a close relative passes away, we make a tear in our clothes to show that we are in mourning. If the priest has such a tear in his clothes for reasons of mourning, he cannot enter the Beit HaMikdash.