A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
jos 3:1JOSHUA COMES TO JORDAN. (Jos 3:1-6)
Joshua rose early in the morning--On the day following that on which the spies had returned with their encouraging report. The camp was broken up in "Shittim" (the acacia groves), and removed to the eastern bank of the Jordan. The duration of their stay is indicated (Jos 3:2), being, according to Hebrew reckoning, only one entire day, including the evening of arrival and the morning of the passage; and such a time would be absolutely necessary for so motley an assemblage of men, women, and children, with all their gear and cattle to make ready for going into an enemy's country.
jos 3:2the officers went through the host; And they commanded the people--The instructions given at this time and in this place were different from those described (Jos 1:11).
jos 3:3When ye see the ark . . ., and the priests the Levites bearing it--The usual position of the ark, when at rest, was in the center of the camp; and, during a march, in the middle of the procession. On this occasion it was to occupy the van, and be borne, not by the Kohathite Levites, but the priests, as on all solemn and extraordinary occasions (compare Num 4:15; Jos 6:6; Kg1 8:3-6).
then ye shall . . . go after it. Yet there shall be a space between you and it--These instructions refer exclusively to the advance into the river. The distance which the people were to keep in the rear of the ark was nearly a mile. Had they crowded too near the ark, the view would have been intercepted, and this intervening space, therefore, was ordered, that the chest containing the sacred symbols might be distinctly visible to all parts of the camp, and be recognized as their guide in the untrodden way.
jos 3:5Joshua said unto the people--rather "had said," for as he speaks of "to-morrow," the address must have been made previous to the day of crossing, and the sanctification was in all probability the same as Moses had commanded before the giving of the law, consisting of an outward cleansing (Exo 19:10-15) preparatory to that serious and devout state of mind with which so great a manifestation should be witnessed.
jos 3:6Joshua spake unto the priests--This order to the priests would be given privately, and involving as it did an important change in the established order of march, it must be considered as announced in the name and by the authority of God. Moreover, as soon as the priests stepped into the waters of Jordan, they were to stand still. The ark was to accomplish what had been done by the rod of Moses.
jos 3:7THE LORD ENCOURAGES JOSHUA. (Jos 3:7-8)
the Lord said to Joshua, This day will I . . . magnify thee in the sight of all Israel--Joshua had already received distinguished honors (Exo 24:13; Deu 31:7). But a higher token of the divine favor was now to be publicly bestowed on him, and evidence given in the same unmistakable manner that his mission and authority were from God as was that of Moses (Exo 14:31).
jos 3:9JOSHUA ENCOURAGES THE PEOPLE. (Jos 3:9-13)
Come hither, and hear the words of the Lord--It seems that the Israelites had no intimation how they were to cross the river till shortly before the event. The premonitory address of Joshua, taken in connection with the miraculous result exactly as he had described it, would tend to increase and confirm their faith in the God of their fathers as not a dull, senseless, inanimate thing like the idols of the nations, but a Being of life, power, and activity to defend them and work for them.
jos 3:14THE WATERS OF JORDAN ARE DIVIDED. (Jos 3:14-17)
And it came to pass, when the people removed from their tents, &c.--To understand the scene described we must imagine the band of priests with the ark on their shoulders, standing on the depressed edge of the river, while the mass of the people were at a mile's distance. Suddenly the whole bed of the river was dried up; a spectacle the more extraordinary in that it took place in the time of harvest, corresponding to our April or May--when "the Jordan overfloweth all its banks." The original words may be more properly rendered "fills all its banks." Its channel, snow-fed from Lebanon, was at its greatest height--brimful; a translation which gives the only true description of the state of Jordan in harvest as observed by modern travellers. The river about Jericho is, in ordinary appearance, about fifty or sixty yards in breadth. But as seen in harvest, it is twice as broad; and in ancient times, when the hills on the right and left were much more drenched with rain and snow than since the forests have disappeared, the river must, from a greater accession of water, have been broader still than at harvest-time in the present day.
jos 3:16the waters which came down from above--that is, the Sea of Galilee
stood and rose up upon a heap--"in a heap," a firm, compact barrier (Exo 15:8; Psa 78:13);
very far--high up the stream;
from the city Adam, that is beside Zaretan--near mount Sartabeh, in the northern part of the Ghor (Kg1 7:46); that is, a distance of thirty miles from the Israelitish encampment; and
those that came down toward the sea of the desert--the Dead Sea--were cut off (Psa 114:2-3). The river was thus dried up as far as the eye could reach. This was a stupendous miracle; Jordan takes its name, "the Descender," from the force of its current, which, after passing the Sea of Galilee, becomes greatly increased as it plunges through twenty-seven "horrible rapids and cascades," besides a great many lesser through a fall of a thousand feet, averaging from four to five miles an hour [LYNCH]. When swollen "in time of harvest," it flows with a vastly accelerated current.
the people passed over right against Jericho--The exact spot is unknown; but it cannot be that fixed by Greek tradition--the pilgrims' bathing-place--both because it is too much to the north, and the eastern banks are there sheer precipices ten or fifteen feet high.
jos 3:17the priests . . . and all the Israelites passed over on dry ground--the river about Jericho has a firm pebbly bottom, on which the host might pass, without inconvenience when the water was cleared off.