Why did God make Israel undergo a national circumcision right after crossing the Jordan?
God required Israel to undergo national circumcision right after crossing the Jordan because they had neglected the rite for 40 years. Though they were in enemy territory near the first city to conquer, God stopped them so that, in dealing with Him, first things would come first.
Les explains that Israel had just crossed the Jordan and was now in enemy territory, only a mile or two from the first city they would have to conquer. At that critical moment, God halted the nation for a national right of circumcision. The reason was that they had neglected circumcision for 40 years. Les points out that when it comes to dealing with God, it is first things first, so this act of obedience had to precede the conquest.