Christ Triumphant: God Performs Miracles for a Reason, May 5

And the priests that bare the ark of the covenant of the Lord stood firm on dry ground in the midst of Jordan, and all the Israelites passed over on dry ground, until all the people were passed clean over Jordan. Joshua 3:17.

At this time of the year—in the spring season—the melting snows of the mountains had so raised the Jordan that the river overflowed its banks, making it impossible to cross at the usual fording places. God willed that the passage of Israel over Jordan should be miraculous....
At the appointed time began the onward movement, the ark, borne upon the shoulders of the priests, leading the van.... All watched with deep interest as the priests advanced down the bank of the Jordan. They saw them with the sacred ark move steadily forward toward the angry, surging stream, till the feet of the bearers were dipped into the waters. Then suddenly the tide above was swept back, while the current below flowed on, and the bed of the river was laid bare....
When the people had all passed over, the ark itself was borne to the western shore. No sooner had it reached a place of security, and “the soles of the priests’ feet were lifted up unto the dry land,” than the imprisoned waters, being set free, rushed down, a resistless flood, in the natural channel of the stream.
Coming generations were not to be without a witness to this great miracle. While the priests bearing the ark were still in the midst of Jordan, twelve men previously chosen, one from each tribe, took up each a stone from the riverbed where the priests were standing, and carried it over to the western side. These stones were set up as a monument in the first camping place beyond the river....
The influence of this miracle, both upon the Hebrews and upon their enemies, was of great importance. It was an assurance to Israel of God's continued presence and protection—an evidence that He would work for them through Joshua as He had wrought through Moses....
This exercise of divine power in behalf of Israel was designed also to increase the fear with which they were regarded by the surrounding nations, and thus prepare the way for their easier and complete triumph.... To the Canaanites, to all Israel, and to Joshua himself, unmistakable evidence had been given that the living God, the King of heaven and earth, was among His people, and that He would not fail them nor forsake them.—Patriarchs and Prophets, 483-485.