וַיֹּ֨אמֶר אֵלָ֤יו יְהוָה֙ לֶךְ־רֵ֔ד וְעָלִ֥יתָ אַתָּ֖ה וְאַהֲרֹ֣ן עִמָּ֑ךְ וְהַכֹּהֲנִ֣ים וְהָעָ֗ם אַל־יֶֽהֶרְס֛וּ לַעֲלֹ֥ת אֶל־יְהוָ֖ה פֶּן־יִפְרָץ־בָּֽם׃
여호와께서 그에게 이르시되 가라 너는 내려가서 아론과 함께 올라오고 제사장들과 백성에게는 돌파하고 나 여호와에게로 올라오지 못하게 하라 내가 그들을 돌격할까 하노라
Rashi on Exodus
לך רד GO, GO DOWN and warn them a second time. God said this, because the rule is that one admonishes a person before an action is to be done and then one again admonishes him at the very moment when the action is to be done (cf. (Mekhilta d'Rabbi Yishmael 19:24:1).
Sforno on Exodus
לך רד, now, when I am speaking with you, be with them at the bottom of the mountain.
Or HaChaim on Exodus
רד ועלית אתה ואהרון, "descend and then ascend, you and Aaron." Why did G'd say both לך and רד? The word לך meant that Moses was to move, the word רד that he was to descend; perhaps he had to descend as he had previously not stood on a place assigned to him on the Mountain but had stood on the peak. When Moses refused to move G'd may have told him to descend (from that peak) but to ascend again with Aaron. He should know that just as there was a limit to how far Aaron could ascend there would also be a limit to how far he, Moses, could ascend. This is implied when the Torah describes Aaron as ascending עמך"with you."