The D’rashos HaRan says that the Urim v'Tumim wasn’t really part of the Bigdei Cohen Gadol, and the fact that Ahron was a Cohen would not be enough of a reason that he should be Zoche to have it. The reason Ahron was Zoche was because: ויִחָא תַלוּדְגִבּ חַמָשֶׂשׁ בֵל his heart rejoiced with his brother’s greatness. Although Ahron preceded Moshe in Nevua, he still had no Kin'ah when Moshe was chosen to be the Navi. That’s why he was Zoche to the Urim v'Tumim, which tells the future like Nevua and in a way even stronger than Nevua, since a prediction of a Navi can be retracted, but a prediction of the Urim v'Tumim cannot.
This reward to Ahron is Midda K'neged Midda. By not having Kin'ah for Nevua, he gets Nevua; and even his children are Zoche to the Urim v'Tumim. R' Tzadok HaCohen Zatzal says that whoever cherishes and holds dear when others do the will of Hashem, even though he himself is not participating [since he can’t] his rejoicing with others doing is as if he himself is doing it.
In Novardok they would say that to be involved in Ayin Tova is a “good business” with plenty of “profit”. How important it is to be involved in the Avodas Hashem of others!
An Ayin Tova is always a happy person, who is filled with Simcha from seeing people he knows succeed.
People who work on Ayin Tova are always praising the people they are jealous of. They have a Geshmak in working on their Middos; and the more jealous they are, the more they Davka praise [or do Chesed with] that person. They learn the appropriate Mussar Seforim, and work on furthering their growth in Bitachon of Hashem, that He created me, and gave me the best possible situation and circumstances for my Shleimus. This Bitachon helps them be extremely happy with their own situation, and easily have an Ayin Tova.
Similarly, in the Bracha on the Torah every morning, we don’t daven only for our own children, but also for the children of the entire Jewish nation as well. The Gr”a says that when a person davens Shmoneh Esrei, he needs to concentrate on the simple meaning, asking Hashem to help all of us.
We were taken out of “Mitzrayim” by two “brothers” [Moshe and Ahron] who were constantly honoring each other. They took us out of “Mitzrayim” which stands for “Tsar Ayin”. [The entire Shi’bud started because a Mitzri couldn't Fargin there were so many strong and beautiful Jews]. The example they set for us, taught us how to have good Middos, so that we truly deserved to leave this place of bad Middos.
