What happens spiritually when a person gets born again?
When a person is born again, they come into a right relationship with God, become a child of God, and partake of living water. At that same time, the old flesh begins war against the new nature, so the spiritual life involves ongoing conflict between flesh and spirit.
Les teaches that Israel's experience in the desert, where the Amalekites fought over the water God provided from the rock, is a picture for believers. Paul says these things are written for our learning, not for doctrine so much, but for practical experience. As soon as a person comes into that right relationship with God—becomes born again, becomes a child of God—they partake of the living water. Then the old flesh begins the war, and the flesh wars against the new nature. The Amalekites picture the flesh warring against the spiritual.