When the apostle Paul wrote to the Ephesian Christians [Eph. 6], he was not suggesting that they view their conflict with the powers of darkness as a battle whose outcome still hung in the balance. He was telling them they needed to “be strong in the Lord, and in the strength of His might” (v. 10, emphasis added); to “stand firm” (vv. 11, 13); to use the spiritual armor – truth, righteousness, the gospel of peace, faith, salvation, and God’s Word – to resist the schemes of the devil. They were to fight from a position of victory, not out of fear that Satan might make them toast.
John MacArthur