In addition to physical death, what must we do to the old Adam?
Beyond physical death, the old Adam—the sin nature centered in mind, will, and emotion—must be put to death spiritually. This happens by faith, appropriating the work of the cross and reckoning him dead in Christ, or he will experience the second death.
Les explains that inside this body of flesh, God placed the invisible part of us—the personality, the I, the id, the ego—centered in the mind, will, and emotion. That mind, will, and emotion we are born with comprises the old Adam. Even though old Adam lives in this body of flesh that is going to die, we also have to appropriate a death to that old Adam, to that spirit side of us. Paul deals with this most. When we talk about old Adam having to die, it means the old sin nature we are born with has to die spiritually—either in this life by appropriating the work of the cross and having Him reckoned as dead in Christ, or old Adam will experience the death knell of the great white throne and be consigned to the lake of fire forever, which is the second death. Everyone will die a physical death if the Lord does not come, but the spiritual aspect is that we either put him to death by faith and the gospel on the cross, or he will experience the second death by virtue of the great white throne and eternal doom.