Why do we need the power of God to energize our spirit?
Because Adam's sin caused the human spirit to die, leaving people spiritually dead and unable to restore themselves. A dead spirit is like a dead battery: cleaning it cannot give life. Only an outside source—God's power—can energize the spirit, making a person a new creation.
Les teaches that Adam's sin immediately made his soul a sin nature, and the spirit part of him died, losing fellowship with the Creator. He illustrates that dead spirit as a dead battery in a car: you can wash and shine the battery, but turning the key still gives nothing because it remains dead. Only outside energy brings power. Spiritually, because we have been dead as a result of Adam's sin, it takes an outside source of power—the power of God—to energize our spirit. When He energizes the spirit, He makes us a new person, or a new creation. Les also notes that as husband and wife become one, so the believer and Christ are one; if any man be in Christ, he is a new man, and you cannot just fix up the old.