The dispute between Rashi and the Ramban seems to reflect a fundamental argument with regard to their understanding of the very nature of a Mishkan. Ramban obviously understands the entire concept of a Mishkan as "l'chatchila" (de jure), for it perpetuates Har Sinai. In contrast, Rashi's basic concept of a Mishkan is "b'di'eved" (de facto), i.e. ideally man should be able to relate to God without any physical representation. We reach this conclusion by Rashi insisting that the commandment to build the Mishkan was given only after Chet Ha'egel. According to this approach, the Mishkan only becomes necessary as a result of the children of Israel's weak spiritual character.