We are told that if we have a difficulty in resolving a dispute among litigants, or if we are unsure about a certain law and we cannot resolve the matter within our community, we should go up to the place that Hashem will choose, namely Jerusalem, and bring the matter before the Kohanim. In the time of the Bet Hamikdash the Kohanim were the leaders and teachers of the people. The decisions of these judges must be followed.
Then the Torah adds and tells us that if a person shall deliberately ignore the bidding of the Kohen HA’OMED LESHARET SHAM ET HASHEM, “who stands there to serve Hashem”, then a proscribed punishment is to be carried out. Why was it necessary to mention the fact that the Kohen serves Hashem? This is well known and unrelated to the instructions on hand.
The fact, however, is that many people think that a Kohen who spends his time in serving Hashem is disconnected from the mundane world and cannot be expected to resolve worldly disputes. Many feel this way also about Rabbis and teachers of religion today. They think that people who are involved in the spiritual world are detached from reality. That is why the Torah emphasizes that one should go to the Kohen who serves Hashem. Specifically, he, is in a better position to judge ethically and morally to resolve the issue on hand.