However, the Torah does not in fact say anything about love when it lays down the kohen’s duty. So what is the source of the statement about love?
The answer could be this. Everything in Judaism derives from two love-obligations – the duty stated in the Sh’ma to love the Lord our God, and the duty in Parashat K’doshim (Lev. 19:18) to love our fellow man.
Whatever we do as Jews is either a duty to God or a duty to other people. When we pray to God, we must do so lovingly. When we support other people, we must also do so lovingly.
The kohen has the same obligations as every other Jew, but with additional responsibilities arising out of his priestly status. One of these obligations is to be the teacher, guide and role model of the community. His efforts for the community are a service to both God and man at the same time.
Like every leader, he might be tempted and influenced by selfish and unworthy motives; when he humbly, solemnly and publicly acknowledges that his service is “in love”, both God and man can be certain that his motivation is pure.