Neil Young had a hit song in the 1970s called "Heart of Gold". Was he singing about Aharon HaKohen? Perhaps, that is why G-d chose Aharon to be the Kohen Gadol and to wear the golden vestments.
The Torah states, "And Aharon shall bear the judgment of the Children of Israel on his heart constantly before G-D" (Shemot 28:30). This verse is a reference to the CHOSHEN-BREAST PLATE, which Aharon wore over his heart. This breast plate was folded in half to form a pocket into which was placed a parchment containing
G-D's Ineffable Name. This was called the Urim VeTumim, which caused the letters of the names of the Tribes of Israel which were inscribed on the CHOSHEN to light up with answers to questions of national importance.
The merit of wearing the CHOSHEN was given to Aharon because of his special character. When he went to greet Moshe, after Moshe had been selected by G-D to lead the Jews out of Egypt, he came with a smile and a glad heart. As the Torah states, "And when he (Aharon) sees you (Moshe) he will rejoice in his heart" (Shemot 4). This remarkable love for a younger brother, who will replace him as leader, was rewarded with the CHOSHEN that Aharon wore over his heart that rejoiced for his younger brother.
Was it so difficult to rejoice for a brother's good fortune? Does Aharon deserve such an amazing tribute just for being happy for his brother? HaRav Nebentzahl, who is sitting shiva for his wife, maintains there are various levels of selflessness. It is one thing to defer to one's brother. It is a totally different level, when a person has been the leader of Israel throughout the years of persecution, pain and sorrow as Aharon was, and to have his younger brother take over, and be happy about it!
This character trait is exceptional and amazing. Aharon had pure selfless joy for Moshe's good fortune, even though he was now demoted from his position of leadership of Israel.
Only a person who possesses such a loving heart, had the merit to wear the BREAST PLATE over his heart.