Set Apart at Sinai and the Hidden Hint of Nadab and Abihu

It was taught: "And also the priests who draw near to the LORD shall sanctify themselves" (Exodus 19:22). Rabbi Joshua ben Korhah says: this refers to the separation of the firstborn. Rabbi says: this refers to the separation of Nadab and Abihu. According to Rabbi this is well, for it is written, "This is what the LORD spoke, saying: Through those near to Me I will be sanctified" (Leviticus 10:3). But according to Rabbi Joshua, who says it refers to the firstborn, where is the separation of Nadab and Abihu hinted? In the verse, "And I will meet there with the children of Israel, and it shall be sanctified by My glory" (Exodus 29:43). Do not read it as "by My glory" [bichvodi], but rather [as bimchubadai, "through My honored ones"]. The Holy One, blessed be He, hinted this matter to Moses, but he did not understand it until the sons of Aaron died. "And the LORD said to him: Go, descend, and then you shall come up" (Exodus 19:24). You have spoken well. This is what Rabbi Judah used to say: From where do you say that the Omnipresent said to Moses, "Behold, I am telling you a thing, and you may answer Me back, and I will concede to you, so that Israel may say, Great is Moses, to whom the Omnipresent conceded"? Rabbi says: We cannot make Moses great unless we make it that the Holy One, blessed be He, retracted His words; rather, one urges a person at the time of study and urges him again at the time of the deed. "And you shall come up, you and Aaron with you, and the priests and the people" (Exodus 19:24). One might think all may ascend; therefore Scripture says, "And the people shall not break through to come up to the LORD." One might think even the priests may go up with you; therefore Scripture says, "And you shall come up." Say from now: just as you make a barrier for yourself, so they too make a barrier for themselves, and the people shall not go up at all. "Lest they break through to come up," lest they push forward.