v1-9: The stones were set up as a testimony to God's power and salvation. It is suggested that they picture baptism, which does not accomplish salvation, but is a visible testimony to salvation. Yet such a testimony is not unimportant, Rom 10.9-10, and is a deeply spiritual thing.
v10: The priests stood in the middle of the Jordan as the people passed over. Jesus Christ's work on the cross enables those who trust in Him to pass from death to life.
v12-13: About 40,000 armed men from Reuben, Gad, Manasseh; this compares with the following (in Num 26.7,18,34); Reuben 43,730; Gad 40,500; Manasseh 52,700. Not all those "able to serve" (Num 26.2) actually did serve.
v14: Joshua's leadership was vindicated; God had chosen Joshua as Moses' successor, and now confirmed that choice.
v15-17 The priests waited until the Lord’s command, just as Noah waited in the ark until the Lord commanded he should leave (Gen 8.15).
v18: As the priests came up from the river, the waters returned. The illustration is of baptism, which is a mark of obedience to God's command.
The crossing of the Jordan marked the end of the 40 years in the wilderness. Where the crossing of the Red Sea pictures redemption, and the crossing of the Jordan pictures baptism, we are cautious in pressing the pictures too far. The 40 years delay was due to disobedience, and does not necessarily represent a Christian's normal experience. However, through disobedience we too will experience a spiritual wilderness, and lack of fruit in our lives.
v19: They crossed over on the 10th day of the 1st month; this was an unusual time for harvest. It is possible that God delayed, or brought forward the harvest, so that the people were fed.
Since Deut 1.3 (1st day, 11th month), there is a period of 69 days. During this period, Moses had explained the law of God, and the people had travelled the last few miles to the Jordan, and then over it.
v22-24: See also v8-9; Joshua set up the twelve stones. These were a testimony to God's power in bringing His people across the Jordan. The nations would realise that the God of Israel was a mighty God. Just like Abraham, there were physical reminders of powerful meetings with God throughout the land. This marked a constant testimony to God's people of His faithfulness.