Question
Is a Kohen who sins allowed to serve in the Temple?
Answer
If a Kohen becomes an apostate, his service is invalid; see Ezekiel 44:12-13. A Kohen who is a chronic sinner should not be allowed to serve (Aruch Ha-Shulchan He-Asid, Bi’as Mikdash 49:8) unless he repents. The Talmud (Berachos 32a) tells us that a Kohen who has committed murder should not bless the people. This would imply that he should not perform any Temple service; but Tosafos (Yevamos 7a) rules that if he does so, the service is valid.