“When Joshua was by Jericho, he lifted up his eyes and looked, and behold, a man was standing before him with his drawn sword in his hand. And Joshua went to him and said to him, “Are you for us, or for our adversaries?” And he said, “No; but I am the commander of the army of the Lord. Now I have come.” And Joshua fell on his face to the earth and worshiped and said to him, “What does my Lord say to his servant?” And the commander of the Lord’s army said to Joshua, “Take off your sandals from your feet, for the place where you are standing is holy.” And Joshua did so.”
Joshua 5:13-15 ESV

Coming to passages like this can be tricky to navigate. The Scripture, here, does not explicitly tell us who the commander of the Lord’s army is. Which leaves us to ask the question: who is this commander, and how is it that He says He takes no sides? What army does He command?

Well, to answer these questions we have to go forward and then come back. It is easy to think of Jesus Christ coming on the scene for the very first time in the Gospel of Matthew. Jesus as the Christ is not mentioned specifically in the Old Testament or as being present in those narratives. However, the New Testament says of Jesus:

“All of them ate the same spiritual food, and all of them drank the same spiritual water. For they drank from the spiritual rock that traveled with them, and that rock was Christ.”
1 Corinthians 10:3-4 NLT

“So I want to remind you, though you already know these things, that Jesus first rescued the nation of Israel from Egypt, but later he destroyed those who did not remain faithful.”
Jude 1:5 NLT

So from these scriptures we can begin to see that the New Testament writers saw Jesus in the Old Testament and from that authority we can conclude that Jesus is present in the word before His manifest presence in the Gospels. That helps us answer what would otherwise be a very tricky question. How is it that God—who the Apostle Paul calls “the invisible God”—can appear to Abraham and Moses, or be spoken to “face to face, as a man speaks to his friend,” or be physically wrestled with by Jacob?
How is it that God can be visible, when God tells Moses, “You cannot see my face, for man shall not see me and live”?

The Apostle Paul puts the answer plainly in his letter to the Colossians:

“Christ is the visible image of the invisible God. He existed before anything was created and is supreme over all creation,”

Colossians 1:15 NLT

These manifestations of Christ are pre-incarnate - meaning it is before Jesus Christ became flesh and dwelt among us. See, no one has seen the Father except the Son; but, those who have seen the Christ have seen the Father. This gives us this understanding: if the people found in the Old Testament and are said to have seen God, they were indeed seeing Jesus Christ. This is known as a Christophany. The word comes from the Greek words “Christos” meaning Christ and “phainein” meaning to appear or bring to light.

Back to the scripture we started with. This then has to be a Christophany because of how the interaction transpired. First, the commander of the Lord’s army is described as man, which would be from Joshua’s perspective. When Joshua questions Him, the commander promptly responds that He is not taking sides but has come in the office of commander. This prompts Joshua to fall face down and worship - something that Joshua would not do to angel; even if he was to worship an angel he would have been rebuked. (See Revelation 19:10) Furthermore, Joshua goes on to call himself servant and awaits instruction. Angels can only do what they are told, for they are messengers and have no authority to change form the instruction. Joshua is then told that the place he is standing is holy ground, something we have seen happen to Moses at the burning bush while talking to the God.

So the commander of the Lord’s army is Jesus and He commands an army of angelic beings (see Matthew 26:53) - perhaps it was the working of the angels that took down the walls of the city!