First, God commands them to circumcise all the men (Joshua 5:2). This is not surprising; it was a standing command for all Israelite males (Genesis 17:10-14); a command the Israelites had not obeyed as they wandered in the wilderness (Joshua 5:5). It is not surprising that God would remind His people of His law. What is surprising is the timing. The Israelites had just crossed the Jordan into the Promised land. They were in hostile territory. Yet, here was God asking the Israelites to do something that would make them unable to fight for a number of days. The Israelites knew the danger. They remembered what Levi and Simeon had done to the city of Shechem (Genesis 34:24-29). But, God had spoken. He required circumcision and obedience is more important than military strategy!
Second, God gave Joshua a very strange battle plan as they approached Jericho (Joshua 6:2-6). Most armies don't conquer cities by marching around the walls (you might get shot) and blowing horns. Yet, that is what God asked the Israelites to do. So they did, and God gave them victory.
Both of these incidents are strange when we stop and think about them. God's instructions seem foolish. Yet, they were God's instructions. They needed to be obeyed regardless of what Joshua and the Israelites thought. That is what faith is; that is what faith does.
God rewarded their faith. During the days of healing after the circumcisions, He protected the army. He made sure that the Canaanites did not attack (Joshua 5:1). He also allowed the Israelites to conquer Jericho, not by arms but by believing God's Word.
How about you? Is there some command of God that you are avoiding because it seems foolish? Today is the day to obey. Commit yourself to God and step out in faith.