Numbers 10:21

נשאי המקדש means, the bearers of the holy articles (not of the structure of the Sanctuary itself for this was the burden of the sons of Gershon and Merari; cf. v. 17). והקימו את המשכן AND THEY SET UP THE TABERNACLE [BEFORE THEY CAME] — this means: The sons of Gershon and the sons of Merari who were in front of them (the Kohathites) travelling together with the two divisions, those of Judah and Reuben, set up the Tabernacle as soon as the cloud rested, and the sign for encamping became visible above the division of the camp of Judah (cf. Rashi on 9:17). Now when they encamped and whilst the sons of Kohath were coming after them with the two last divisions (Ephraim and Dan), the sons of Gershon and the sons of Merari erected the Sanctuary. When the sons of Kohath arrived, they already found it in its proper place and they put into it the Ark, the table, the candelabrum and the altars. The following therefore is what the verse implies: והקימו, and they — i.e. those who had to erect the Tabernacle — erected it, עד before באם their arrival — the arrival of the sons of Kohath.

וְנָסְעוּ֙ הַקְּהָתִ֔ים נֹשְׂאֵ֖י הַמִּקְדָּ֑שׁ וְהֵקִ֥ימוּ אֶת־הַמִּשְׁכָּ֖ן עַד־בֹּאָֽם׃

And the Qehati set forward, bearing the sanctuary: that they might set up the tabernacle against their arrival.