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.