EXOD85 We must be happy for the good fortune of others. The Midrash (Shmos Rabbah 3:17) states that Aharon merited wearing the breast plate, which was worn by the High Priest when he served in the Holy Temple, as a reward for his unreserved happiness in greeting Moshe. Aharon might have felt jealous that his younger brother was chosen as the leader, but instead he was full of joy over his brother's success. From here we see that even the greatest of people can be guilty of jealousy, and it is considered a merit on their part if they refrain from being jealous. We must try to cultivate the attitude of happiness at the good fortune of others. Chochmah Umussar, vol. 2, essay 234.