Speak unto all the congregation of the children of Israel,.... They could not be all spoke to together, but tribe after tribe, or family after family; or rather the heads of the tribes, and at most the heads of families were convened, and the following instructions were given, to be communicated to their respective tribes and families.
Jarchi says this section was spoken in the congregation, because the greater part of the body of the law, or the more substantial parts of it, depend upon it; and indeed all the ten commandments are included in it, with various other laws, both judicial and ceremonial.