Albert Barnes Commentary Joshua 3:7

"And Jehovah said unto Joshua, This day will I begin to magnify thee in the sight of all Israel, that they may know that, as I was with Moses, so I will be with thee." — Joshua 3:7 (ASV)

This day will I begin to magnify thee — One reason why the miracle about to be described was performed is suggested here. Just as Moses was declared to be sent directly from God with an extraordinary commission by the miracles he performed, especially that of dividing the Red Sea into two parts, so Joshua was both sent and accredited in a similar manner. (Compare Joshua 1:5 and Joshua 4:14.) Other reasons are given in Joshua 3:10; Joshua 5:1.