Bro. R.--In what sense do you consider Christ our substitute? Since you believe that when the Saints are made immortal they give up their flesh life as Christ gave up his, they needed no substitute. And since the sinner will die the second death it cannot be that he has a substitute.
Ans.--I seldom use the word substitute now because it does not occur in our English translation of the Bible, I prefer to use the bible words purchase and ransom which mean exactly the same thing. All men were sinners through Adam's disobedience. The seeds of sin and its result death had been sown in our race and we daily became more weak and sinful. All must die, and the process--"dying thou shalt die" is in progress. There is no way by which we can keep ourselves alive, much less make ourselves alive when we become entirely dead. We can never justify ourselves to life, consequently can never live again.
At this juncture Jesus steps in-- Does he set aside the Father's law which had condemned all the sinful race to death? No, but recognizing death as the righteous penalty of sin; he paid that penalty for us. Being, "without sin," "holy," "undefiled," he was not liable to the penalty of sin--death. He had a perfect right to continue his earthly life forever; but instead he gave it for, i.e., instead of ours that had been forfeited. So that now God can give back perfect natural life to the whole race, and he declares that he will do so in His "due time." Thus did Jesus make himself "a propitiation --[satisfaction] for our sins, and not for ours only, but also for the sins of the whole world, so that, as death passed upon all the human race through Adam, life is to be restored to all in "the times of restitution of all things," because Jesus Christ "gave himself a ransom for all men."
Jesus informs His church of the purchase and tells them that soon all will be restored, but offers to admit them to the Spiritual plane of life if they will now freely give up the natural life--make a sacrifice of it. They could not offer a sacrifice of their natural life until it was purchased for them, because they were already dead. Jesus purchased our lives, then hands them to us saying: Do what you wish with them--here is the great prize, if you crucify yourselves. And we do so gladly for the prize set before us in the Gospel--For ye were bought with a price, even the precious blood of Christ.
What about the sinner who will die the second death? We answer, the fact that he dies the second death on account of his own sins is clear proof that he must have been ransomed from the first death which was the result of Adam's sin.