Joshua 3:10
And Joshua said, Hereby ye shall know that the living God is among you, and that he will without fail drive out from before you the Canaanites, and the Hittites, and the Hivites, and the Perizzites, and the Girgashites, and the Amorites, and the Jebusites.
The stopping of the waters of the overflowing Jordan was the sign by which Israel would know that the living God was among them. That sign guaranteed that He would act for them by without fail driving out from before them the Canaanites, and the Hittites, and the Hivites, and the Perizzites, and the Girgashites, and the Amorites, and the Jebusites. The promised conquest was joined to His presence and power, made evident as the ark led the people into the river.
Christ, accompanied by angels, went before the ark toward the Jordan. Christ and the angels then remained with the ark and the priests standing in the riverbed until all Israel had crossed over.