When Joshua meets the commander of the army of the Lord, He is standing with His drawn sword in His hand. This is a military conquest, a war against flesh and blood. In Revelation 19, this same commander sits on His horse with His sword in His mouth. This is not a war against flesh and blood. Christ rides forth killing men and conquering the nations by His gospel.
We know that our old self was crucified with him in order that the body of sin might be brought to nothing, so that we would no longer be enslaved to sin.