John Calvin Commentary 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 Canaanite, and the Hittite, and the Hivite, and the Perizzite, and the Girgashite, and the Amorite, and the Jebusite." — Joshua 3:10 (ASV)

By this you will know, etc. He makes the power of the miracle extend further than to the entrance of the land, and deservedly so. For merely to open up a passage into a hostile territory, from which there was afterward no retreat, would have been nothing else than exposure to death. For either entangled in straits and in an unknown region, they would easily have been destroyed, or they would have perished, worn out by hunger and the absolute want of all things. Joshua therefore declares beforehand that when God would restore the river to its course, it would be just as if He were stretching forth His hand to rout all the inhabitants of the land, and that the manifestation of His power given in the passage of the Jordan would be a sure sign of the victory which they would obtain over all the nations.

He says, From this you will know that the Lord is present with you; to what end? Not only to plant your feet in the land of Canaan, but also to give you full possession of it. For surely, when mention is made of the overthrow of the nations, an ultimate, free, and peaceful possession is implied. Therefore, as the Lord by dividing the river clearly showed that His power resided with the Israelites, so the people must on their part have conceived hopes of perpetual assistance, as much as if they had already seen their enemies defeated and lying prostrate before them.

For God does not abandon the work of His hands midway, leaving it maimed and unfinished (Psalms 138:8). When He leads His people to the promised inheritance, He makes a dry passage for them by cutting off the course of the Jordan. How perverse then would it have been for the Israelites to stop short at that momentary act, instead of feeling confident for all time to come, until quiet possession of the land was actually obtained! Let us learn then from this example, prudently to combine the different acts of divine goodness relating to our final salvation, so that a happy commencement may cherish and keep alive in our minds the hope of an equally happy termination.

When Joshua says that the people will know the presence of God from the miracle, he indirectly upbraids them for their distrust, as the mere promise of God ought to have sufficed for full assurance, and our faith, unless founded solely on this promise, must be continually wavering. But although faith ought properly to rest on the truth of God alone, it does not follow that experiential knowledge may not act as a secondary support to its weakness and provide subsidiary aid for its confirmation. For what God promises to us in word He seals by His actions; and as often as He shows us manifestations of His grace and power, He intends them to be so many confirmations of what He has spoken, and so many aids tending to suppress all our doubts.