Myśl Żydowska do Samuela I 2:27

Though the general principles, and details, and implications of the G-dly Torah were stated by Moses, this mitzvah [of the Paschal lamb], which is the first that was commanded to Israel, was stated to both [Moses and Aaron]. For both were instrumental in the redemption from Egypt, for which reason it was only fitting that they share jointly in the mitzvah whose cause and underlying idea is the redemption. In addition, the prophecy of Aaron preceded that of Moses, as stated to Eli [the high priest] (I Samuel 2:27): "Did I not appear to the house of your father [Aaron] when they were in Egypt in the house of Pharaoh?" The allusion is to the parshah in Ezekiel (20:7) prophesied by Aaron in Egypt (Shemoth Rabbah 3:16) . And when the Blessed One remembered our ancestors for the good foretold them, to redeem them from the servitude and exile of Egypt, Moses was selected for this task. But he, in his great humility, shrank back from this exalted embassy. Add to this his statement that because he was "heavy of mouth and tongue" it would not serve the honor of the Holy One for him to be the Blessed One's emissary to the Jews and to the king of the nations, as it is written (Exodus 4:10): "…for I am heavy of mouth and heavy of tongue." And the Blessed One's response to this was (Ibid 14): "Do I not know that Aaron, your brother, the Levite, will speak? And he is even now coming out to meet you, and he will see you and be happy in his heart." That is, I know the excellence of his qualities, that he will not take the least offense at your being the head of the L rd's embassy and his being only the spokesman. "And he is even now coming out to meet you." That is, not only is he not offended by this, but when he sees you in this eminence he will rejoice in his heart. Our sages of blessed memory have already remarked upon this as being a great quality in Aaron, for which he was duly rewarded, viz. (Shabbath 139b): "As a reward for 'and he will see you and he will rejoice in his heart,' he merited the breast-plate of judgment upon his heart." And because Aaron did not envy Moses' having been chosen for prophecy, though he preceded him, the Blessed One honored him by having them share jointly in the first mitzvah.