Or HaChaim on Numbers 17:5/אור החיים על במדבר י״ז:ה׳

1 למען אשר לא יקרב איש זר "in order that a non-priest should not approach, etc." Why did the Torah add the words "and so that he shall not become like Korach?" Sanhedrin 110 derives from these words that if someone helps a quarrel to continue he is guilty of transgressing a negative commandment. In addition to this interpretation in the Talmud the Torah may have wanted to explain why it had to recall to people, זכרון, what happened to Korach who brought an unauthorised offering, and why it was not sufficient to merely forbid such offerings in the normal manner and to warn of the death that had befallen Korach. People would not be frightened by this. They would consider it an exceptional occurrence. Only the addition of the word זכרון would impress upon them how seriously G'd viewed the offence of someone arrogating to himself the privileges reserved for the priests.

2כאשר דבר ה׳ ביד משה לו, "as G'd had said to him by means of Moses." The wording of this verse reveals that when Moses had told Korach that G'd would create something new and that he would descend into the bowels of the earth after the earth would split, he had not said this until G'd Himself had told him so. Had the Torah not written this we would have thought that Moses initiated this thought and that G'd did his bidding.