Joshua then said to them, “Do not fear or be dismayed! Be strong and courageous, for thus the LORD will do to all your enemies with whom you fight.”
Joshua and Israel made a treaty with the Gibeonites and five kings banded together immediately afterward to attack Gibeon. So Joshua and Israel came and attacked those kings and God laid a whooping down on those kings and their armies. The kings themselves hid in a cave out of which Joshua had them dragged when the fighting was done. Joshua then had the war leaders in Israel place their feet on the necks of those kings and spoke today’s verse while the war leaders had their feet on those kings.
I’m not going to pretend that what Joshua says is some kind of promise to all believers, because that would be taking the verse wildly out of context. But a similar principle is put forth in the New Testament. Paul tells believers that we wrestle not against flesh and blood. Israel was in a physical battle while the believer in Christ is fighting a spiritual war. Our enemies are not human beings. Our enemies are our sinful nature that must be put to death daily and a world system that is contrary to God’s will and Law and spiritual foes that will try to tempt us away from faith in God and obedience to Him. Paul also instructs the believer to suit-up for spiritual battle by putting on spiritual armor (Ephesians 6) and standing firm. Another place, the way it is expressed is that the believer should resist the devil and he (the devil) will flee. The culmination of all the verses on spiritual warfare is, to my mind, when the believer is told that the One Who lives in us is greater than the one who is in the world. Ultimately, God can guarantee victory in spiritual war just as Joshua was able to guarantee victory over the people living in the Promised Land and for the same reason. Joshua guaranteed his soldiers victory because of God. Notice that he says that the LORD will be the One Who places enemies beneath their feet. It is God Who grants victory in spiritual warfare, as well.
Does Joshua’s promise extend to me? No. But the principle is extended to every believer with regard to spiritual warfare. God is able to put every spiritual foe beneath our feet; to make every spiritual enemy fall before us. For that to happen, I need to remember the first thing Joshua tells those leaders, “Do not fear or be dismayed! Be strong and courageous.” I need to be strong in the LORD and courageous where He tells me to go.