This sanctifying the people meant to set themselves apart from all worldly concerns. It is suitable and proper to withdraw from communion with men, in order to enjoy communion with God. And when our God is about in a more especial manner to come to bless his people, well may they be found waiting the Lord's approach. James 4:8.
Related Commentaries of Joshua 3:5
Joshua 3:5
5 And Joshua said unto the people, Sanctify yourselves: for to morrow the LORD will do wonders among you.