The pasuk (36:7) says that after all the donations were made to the Mishkan they had enough (Dayum). At the end of this pasuk it says “V’Hoseir” and there was even more than they needed. So which is it; was it exactly enough or did they have extra?
If there was exactly enough and no more, each person would become full of pride thinking that his contribution to the Mishkan made it all possible. “Without me there would be no Mishkan”. This would make the Mishkan a place where Hashem’s Shechina would definitely not rest since Hashem does not dwell among the haughty.
However if there was more than enough materials and some were left out of the actual building then each person would be broken hearted thinking that his contribution may have been left out and he has no share of the Mishkan. This made for the ideal sanctuary for Hashem’s Shechina as it always finds rest among the broken hearted.
Therefore the pasuk tells us that the amount of materials donated was exactly enough to build a Mishkan for the Shechina. Why? Because there was excess.