How can believers be counted as crucified with Christ when they were not alive then?
God, in His omnipotence, saw every believer in Christ when Christ hung on the cross and died. Because believers were reckoned in Him, His death is counted as theirs, so they are counted crucified with Christ. This is substitutionary and rests on Christ's finished work, not on their own faithfulness.
Les teaches that old Adam has been put to death, crucified, and his power over daily behavior has been broken. Paul says, “I have been crucified with Christ, yet nevertheless I live; not I, but Christ liveth in me.” God does not take us out when He saves us; He leaves us here to face the pressures and things of this world, and old Adam is still in force experientially. But God reckons him dead. The life now lived in the flesh is lived by the faith, or better, the faithfulness of Christ, because of what Christ accomplished on our behalf and what He is to us day by day. When Christ hung on that cross and died, God in His omnipotence saw every believer in Christ, and that is how we are reckoned as crucified. It is substitutionary and has to be an act of God.