What does the Pasuk mean when it states that "the Melachah was enough for all the Melachah ... "?
Rashi #1 and Seforno: It means that the Melachah of bringing the donations was sufficient for the Melachah (materials) required to construct the Mishkan.
Rashi #2 (in Shabbos 49b, according to the first Lashon in the Gemara): The work that they did for the Mishkan, such as beating out the gold plates to cover the planks and spinning the goats's-hair, was sufficient for the construction of the Mishkan.
R. Bachye: Compared to the work that needed to be done, the work done was more than enough.
Why does the Torah add a 'Mem' to the word "Dayam"
Rashbam: The Torah does this sometimes, like we find regarding the word "Reikam" (Bereishis 31:42) and "Vat'hi ha'Kinam" (8:13)
What is the significance of the fact that they donated more than what was required?
Ramban: Refer to 36:4:1:1.
Seforno: As a result, it was no longer necessary to work sparingly, in case they ran short of material.
"ve'ha'Melachah Haysah Dayam ? Vehoser". Having informed us ? in Pasuk 5 "Mrbi ha'Am Lehavi ? ", why does the Torah insert the current Pasuk?