Every argument which is for the sake of Heaven — the end is [for the parties to that argument] to endure, [as in the argument between Beth Hillel and Beth Shammai, where none of the parties to the argument (the disciples) were lost (as opposed to Korach and his congregation, who were lost). Or: "the end" — the desired end of the argument. In an argument for the sake of Heaven, the desired end is to attain the truth. And this was attained in the argument between Beth Hillel and Beth Shammai — that the halachah is in accordance with Beth Hillel.] And an argument which is not for the sake of Heaven — the [desired] end, [power and love of conquest,] does not endure. [And so we find in the argument of Korach and his congregation. Their end was the attainment of glory and power — and the opposite was what transpired.] What is an argument for the sake of Heaven? The argument between Hillel and Shammai. And (what is an argument) that is not for the sake of Heaven? The argument of Korach and his whole congregation.
Kli Yakar
“And God called the firmament Heaven.” God did not want it to be called by the name “rakia” [firmament] because this name indicates separation and division, as per and they flattened the gold into thin plates (Exodus 39:3) — for that which was to cover the earth. Since any rakia is a covering that separates between two things, and for this reason, it does not state “that it was good” on the second day, since disagreement was created on it, since there is no good except in a place where we find unity. And therefore on the third day, “that it was good” is stated twice: once for the work of the third day and once for the finishing of the water, that has an aspect of unity in it, as it is stated, let the waters gather to one place (Genesis 1:9), and because of this unity, “that it was good” is mentioned. But on the second day — from which comes out all differences, and which is the beginning of all difference and disagreement — “that it was good” was not said about it. And God did not want that [the sky] should be called firmament, which indicates a cover that separates and divides between brothers, and it was called with the name heavens [shamayim], which indicates peace, since shamayim is composed of the words fire [esh] and water [mayim], who made peace between themselves and joined together, and from them was created heavens. And this is what the Rabbis, of blessed memory, state (Avot 5:17), “Any disagreement that is for the sake of the heavens [shamayim], etc.,” which means to say that a disagreement whose purpose is peace, as is the teaching of the name shamayim, and [this is] easy to understand. And according to its simple meaning, “that it was good” was not stated on the second day, since there was no new creation on it, since the firmament was already created on the first day, and the reason for [no creations happening on the second day] is because the second day is the beginning of all difference and division; hence the Holy One, blessed be He, did not want to implant a nature of difference in any creation.