Vayikra: Chapter 60
"When a ruler has sinned"

Rabbi Yitzchak wonders why it is implied that a ruler will sin while a priest might sin. Rabbi Shimon explains that a ruler will sin through the pride of knowing that all the people are under his charge - the matter of his sinning is not in doubt. This is why the gift of stones to be placed on the Efod and the breastplate over the priest's heart must be brought by the rulers and not by other men. In this way the rulers atone for themselves.