Paul knew that if he was faithful to God then there was no way the devil could win this battle. If God chose to let him live, then Paul would live for Christ, and if God chose to take him home to heaven, then he knew that was the ultimate promotion and his faith would end in sight. When we are believers, the devil cannot win. In fact, the devil has already lost because victory was won through the cross and the empty tomb. We still have a few things to wrap up in this dispensation, but the victory has already been won. Whether we live or die, we are the winners and Satan is still defeated.
