“When a person of you will bring close an offering...”. The Alter Rebbe reads that to mean that the offering is brought “of you,” from the heart and soul of the person himself. We see this also in this week's parsha (7:29-30) where the person who offers the sacrifice must bring it himself, with his own hands.
Here we might start to see why sacrifices fit such a central role in the people's story. Back in Sefer Shemot, the sin of the golden calf came inexplicably right after the revelation – how could the people drop to such deep low immediately after such great heights? But the 19th century Hasidic Rabbi Mordechai Leiner ('the Ishbitzer') points out that the people had yet to work for anything or contribute anything to their own liberation. Without the struggle and toil, all their gains were totally insecure and transient. Ever since then the people have been asked to give more and more, combining to contribute all the pieces of the Mishkan. Now with the Mishkan constructed, they are told how to develop a social order where contributing is literally at the center. As we'll see later in Sefer Vayikra, the contributing of sacrifices will form the basis for a society that is called on to even higher tasks – to be a holy people and to love your neighbor as your self.