John Calvin Commentary Joshua 3:2

"And it came to pass after three days, that the officers went through the midst of the camp;" — Joshua 3:2 (ASV)

And it came to pass after three days, etc. That is, three days after their departure had been indicated. For they did not stop at the bank longer than one night. But as the period of three days had previously been set for crossing, and they had no hope of being able to accomplish it, Joshua now exhorts them to disregard obstacles and difficulties, and to focus on the power of God.

For although the form of the miracle is not yet explained, yet when the ark of the covenant is brought forward like a banner to guide the way, it was natural to infer that the Lord was preparing something unusual. And while they are kept in suspense, their faith is again tested by a serious trial; for it was an example of rare virtue to give implicit obedience to the command, and thus follow the ark, while they were obviously unaware of the outcome.

This, indeed, is the special characteristic of faith: not to curiously inquire what the Lord is to do, nor to subtly dispute how what He declares can possibly be done, but to cast all our anxieties upon His providence and, knowing that His power, on which we may rest, is boundless, to raise our thoughts above the world, and embrace by faith what we cannot comprehend by reason.