Joshua 3—4 gives us three reasons why the Lord dried up the Jordan River:
To exalt Joshua in the eyes of Israel (Joshua 3:7);
To demonstrate to the people that the Lord is the living God and that he must be feared by them (Joshua 3:9; Joshua 4:24); and
So that the peoples of Canaan would know that the Lord is mighty (Joshua 4:24; Joshua 5:1).
1 Then Joshua rose early in the morning and they set out from Shittim. And they came to the Jordan, he and all the people of Israel, and lodged there before they passed over.