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?”
(Joshua 5:13-14 ESV)

First, notice that the angel Joshua encounters is not a beautiful woman in a choir robe. Armor-clad soldiers is one of the things History’s The Bible got right.

Secondly, notice he doesn’t say he is on Joshua’s side. He is the commander of the army of the LORD, and Joshua is his servant. Where do we get the idea that God is ever on our side? We don’t even have a side. If you recall, it is later Joshua who says to the nation of Israel “Chose this day whom you will serve… But as for me and my house we will serve the LORD.”