כַּֽאֲשֶׁר דִּבֶּר ה' בְּיַד־משֶׁה לֽוֹ - As God spoke through Moses (lit.) to him. לוֹ is the equivalent of עָלָיו “about him,” i.e., about Aaron He spoke to Moses that he and his sons should be priests; therefore “no layman, who is not descended from Aaron, may approach….” Likewise, every לִי, לוֹ, and לָהֶם that follows the verb דבר (“to speak”) is to be explained in the sense of עַל “concerning.” And its Midrashic explanation is that לוֹ refers to Korach. And why does it say בְּיַד מֹשֶׁה “through Moses” rather than אֶל מֹשֶׁה “to Moses”? It is an allusion to the fact that those who challenge the priesthood are punished with tzara’at, just as Moses was stricken on his hand (בְּיָדוֹ), as it says: “When he withdrew it, his hand became afflicted with tzara’at, white as snow,” 2 and for this reason, too, Uziyah was punished with tzara’at.