The Lord said to Joshua, “See, I have given Jericho into your hand, with its king and the valiant warriors. You shall march around the city, all the men of war circling the city once. You shall do so for six days. Also seven priests shall carry seven trumpets of rams’ horns before the ark; then on the seventh day you shall march around the city seven times, and the priests shall blow the trumpets. It shall be that when they make a long blast with the ram’s horn, and when you hear the sound of the trumpet, all the people shall shout with a great shout; and the wall of the city will fall down flat, and the people will go up every man straight ahead” (Joshua 6:2-5).

The Bible does not directly reveal the reason why God commanded Israel to do what they did in the taking of Jericho, so what I share here is only thoughtful conjecture at best. 

Two things that seem always true in all God's dealings with Israel are these. First, God is most interested in His glory. He does everything to exalt His great Name. I believe this is why the Captain of the host of the LORD tells Joshua that He is neither for nor against Israel (Joshua 5:13-14). It is for His own great Name that He acts. Also, when Israel loses to Ai in battle, Joshua appeals to God's Name: "And what will You do for Your great name?” (Joshua 7:9).

So then, when the LORD commanded Israel simply and quietly to walk around the fortified city, I surmise that this too was so that God might be glorified. I daresay, this approach had never before been recorded as part of any military strategy against a nation. Why? Because it was NOT a military strategy. There is no rhyme or reason for the walls of Jericho to have fallen down from what Israel did, except by God's power. Therefore, as often as the story is told, people have always correctly attributed the victory in Jericho to God. 

Second, God is also keenly interested in careful obedience to His commands. In just about every dealing of God with His people we find that God commands obedience. When God commissioned Joshua to lead His people, He commanded him to carefully obey His Word (cf. Joshua 1:8). Later, when Joshua complained to God about Israel's loss to Ai, God told him that it was because someone in Israel broke His command (cf. Joshua 7:10-11). 

Likewise, I believe God was very interested in seeing how carefully Israel would follow His seemingly absurd military strategy. Would they wordlessly walk around the city? Would they follow the order God directed and blow the trumpets? Would they keep doing this for seven days without grumbling or complaining? I believe that if God asked them to hop like bunnies around the city, they would have done this as well. It was not what they did but that they obeyed God. As they obeyed God, they glorified God in their obedience. 

So, why did God make Israel walk around Jericho thirteen times over seven days? I think it would be a mistake to dissect the method to discover the reason. The larger point seems to point to the timeless truth that (1) God always acts for His glory and (2) God demands careful obedience to His Word. 

Now it came about when Joshua was by Jericho, that he lifted up his eyes and looked, and behold, a man was standing opposite him with his sword drawn in his hand, and Joshua went to him and said to him, “Are you for us or for our adversaries?” He said, “No; rather I indeed come now as captain of the host of the Lord.” And Joshua fell on his face to the earth, and bowed down, and said to him, “What has my lord to say to his servant?” The captain of the Lord’s host said to Joshua, “Remove your sandals from your feet, for the place where you are standing is holy.” And Joshua did so (Joshua 5:13-15).

There are two reasons this may be a theophany (i.e. appearance of God), and likely a Christophany (i.e. a pre-incarnate appearance of Christ). First, Joshua worshipped this "Captain of the host of the LORD". Angelic beings would not have received Joshua's act of worship but would have directed all worship to God and Christ (cf. Revelation 19:10; 22:9). Second, they would not have claimed for themselves the divine presence, making the ground around them holy and prompting Joshua to remove his shoes (cf. Exodus 3:4-6).

What is more, in Revelation 19, the rider on a white horse, whose name is "the Word of God" and "King of Kings and Lord of Lords" is described as the leader of the armies of heaven. Most theologians understand this rider to be Jesus. Paul writes,

The Lord Jesus will be revealed from heaven with His mighty angels in flaming fire, dealing out retribution to those who do not know God and to those who do not obey the gospel of our Lord Jesus (2 Thessalonians 1:7-8).

These texts reveal Jesus as leading the armies of heaven, thus, the title "Captain of the host of the LORD" seems an appropriate title for Him.

Then the Lord said to Joshua, “Today I have rolled away the reproach of Egypt from you.” So the name of that place is called Gilgal to this day" (Joshua 5:9).

There are some differences of opinion on what is meant by "the reproach of Egypt"; however, only Keil and Delitsche provides a defense based on parallel usage in other biblical texts, which I find provides the most compelling evidence. Therefore, this is the view I present here:

When the circumcision was completed, the Lord said to Joshua, "This day have I rolled away the reproach of Egypt from off you." "The reproach of Egypt" is the reproach proceeding from Egypt, as "the reproach of Moab," in Zephaniah 2:8, is the reproach heaped upon Israel by Moab (cf. Isaiah 51:7; Ezekiel 16:57). We are not to understand by this the Egyptian bondage, or the misery which still cleaved to the Israelites from Egypt, and the still further misery which they had suffered during their journey, on account of the displeasure of Jehovah (Knobel), but the reproach involved in the thoughts and sayings of the Egyptians, that Jehovah had brought the Israelites out of Egypt to destroy them in the desert (Exodus 32:12; Numbers 14:13-16; Deuteronomy 9:28), which rested upon Israel as long as it was condemned to wander restlessly about and to die in the wilderness. This reproach was rolled away from Israel with the circumcision of the people at Gilgal, inasmuch as this act was a practical declaration of the perfect restoration of the covenant, and a pledge that the Lord would now give them the land of Canaan for their inheritance. From this occurrence the place where the Israelites were encamped received the name of Gilgal, viz., "rolling away," from גּלל, to roll. This explanation and derivation of the name is not to be pronounced incorrect and unhistorical, simply because it merely preserves the subordinate idea of rolling, instead of the fuller idea of the rolling away of reproach. For the intention was not to form a word which should comprehend the whole affair with exhaustive minuteness, but simply to invent a striking name which should recall the occurrence,