וַיַּ֧עַשׂ בְּצַלְאֵ֛ל אֶת־הָאָרֹ֖ן עֲצֵ֣י שִׁטִּ֑ים אַמָּתַ֨יִם וָחֵ֜צִי אָרְכּ֗וֹ וְאַמָּ֤ה וָחֵ֙צִי֙ רָחְבּ֔וֹ וְאַמָּ֥ה וָחֵ֖צִי קֹמָתֽוֹ׃
And Bezalel made the ark of acacia-wood: two cubits and a half was the length of it, and a cubit and a half the breadth of it, and a cubit and a half the height of it.
Rashi on Exodus
ויעש בצלאל AND BEZALEL MADE [THE ARK] — Because he gave himself over to the work more whole-heartedly than the other wise men it is called after his name (his name alone is associated with the act) (Midrash Tanchuma, Vayakhel 10).
Rabbeinu Bahya
Siftei Chakhamim
Because he extended himself for the work . . . I.e., throughout the section it is written, “He made,” but it is not written “Betzalel” as it does about the ark. This is because they [the other items] do not have as much sanctity as the ark, so Betzalel did not wish to exert himself as much in making them. Instead, Betzalel showed Oholiav and the other disciples [what to do], and they made them. But the ark possessed great sanctity, so Betzalel personally exerted himself over it and extended himself more for the work.