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. Aben Ezra remarks, that all the congregation are spoken to, to include the proselytes, because they had been warned of incests, as the Israelites, in the preceding chapter, (See Gill on Leviticus 18:26); and say unto them, ye shall be holy:
a separate people from all others, abstaining from all the impurity and idolatry they are cautioned against in the foregoing chapter, and observing the holy precepts expressed in this: for I the Lord your God [am] holy;
in his nature, essence, originally, independently, immutably, and perfectly; and the more holy they were, the more like they would be to him; (See Gill on Leviticus 11:44) and (See Gill on Leviticus 11:45); where the same words are used, after the laws given about creatures clean and unclean to be eaten, as here, after those about impure copulations and incests.