John Calvin Commentary Joshua 3:6

"And Joshua spake unto the priests, saying, Take up the ark of the covenant, and pass over before the people. And they took up the ark of the covenant, and went before the people." — Joshua 3:6 (ASV)

And Joshua spoke to the priests, etc. It is probable that the priests were informed why God wanted the ark to go before them, so they would be more prepared to carry out the command, since the whole people were immediately afterward made aware of the intended division of the waters. Since the officers had previously announced in the camp that the people were to follow the ark of the covenant, the priests could not possibly have been unaware of the duty they were to perform. For it had been clearly stated that they were to be leaders or standard-bearers.

But when all were ready, Joshua publicly revealed the divine message he had received. For it would have been unfitting to reveal God's favor more clearly to the common people than to the priests. It is added, however, immediately afterward, that the people were made aware of the miracle.

I conclude, therefore, that after the priests had been kept in suspense for some time, along with the multitude, the Lord, upon confirming the obedience of all, publicly declared what He was going to do. First, then, it is related that Joshua commanded the priests to carry the ark before the people; and secondly, so that no one would think he was making the attempt randomly or on his own initiative, the promise he had been given to support his command was also mentioned.

But although it is not then clearly stated that the course of the Jordan would be stopped, yet, from the words Joshua used to the people, we may infer that the Lord spoke in more detail and explained more clearly what He had decided to do. For Joshua did not mention anything that he had not previously learned from the mouth of God Himself. Indeed, before he mentions the matter at all, he tells them to hear the words of the Lord, and thus begins by stating that he has God's authority for what he is about to say.