The ears have lobes which can be used to block the entrance of unseemly words. The eyes have lids and brows. Thus it is with all the organs of perception. With one exception. The mind has no protection.
Thoughts have no visor.
They can come and go at will. Therefore it takes an extra degree of alacrity and alertness to guard against improper thoughts. Chisaron kis' can mean literally 'a loss of pocket' - a monetary loss. In most offerings, the kohanim were given part of the animal to eat. However, in the Korban Olah , where the entire of offering was burned and the kohen received nothing, the kohanim needed to be commanded an extra degree of alacrity.