I. The Position of Man and the Justice of God
From nearly the beginning of man's existence, he has been a polluted creature. From the moment Adam gave his nature over to rebellion, man's bloodline has been corrupted. We, all being sinners, owe a fantastic debt. God, being just, must see the demanded price of man's debt paid in full. That price (the price of reconciliation with the unblemished, incorruptible King of Creation) is eternal separation.
Now only two possibilities can satisfy God's justice in this regard that is, the hope of payment can only come from two possible sources. Since the debt must be paid God cannot simply remove the penalty and the price cannot be justly laid on the head of another without his consent, only two options remain: 1) one man could volunteer to take the punishment of another onto his own head or 2) God could take the debt upon Himself. Yet while either of these possibilities will satisfy God in His justice, justice is not the only requirement to be filled.
II. Purity and the Sacrifice
When we inquire of the stature of any possible benefactor, we first find the potential substitute must actually have the ability to pay the debt. If two men are led to the gallows for capital crimes, the first stands in no position to take the penalty of the second upon himself as well as his own. So is the case with man. All of us have "fallen short" and are in no position to offer ourselves to the hangman in the place of another. This fact narrows the list of potential candidates to the unfallen angels and God Himself (both of whom are holy and free from the penalty of sin).
III. Infinitude and the Atonement
Now to further and finally narrow our range of possibilities, the only way that any potential substitute's sacrifice could be sufficient is if that substitute were infinite. The sacrifice of any one perfect being would only suffice to cover one man's sin and then, only one of that man's sins. Jesus Christ died for the world a world that is even now sinning. For that to be accurate, He would have to be infinite. But there can only be one infinite and that is God Himself. Therefore, if Christ did truly pay for sins as an atonement, He must be God.
IV. Only a Man's Blood
Looking further at the redemption of man, we find one final clue to the identity of Christ; we must focus on His method of payment. As an example, imagine a man is incarcerated in an American debtor's prison and the Emperess of Venus wanted to pay my debt and free me. Suppose she arrives with millions of dollars in cold, hard Venusian cash to make the payment. Her payment would not be accepted in that form; such debts must be paid in the coin of the realm. In the man of our example's case, laguishing in the debtor's prison, that coin would be the American currency; in humanity's case, the coin of the realm is blood. Not just any blood: man's blood. That is the price for mankind human blood for human souls. For our redemption to be possible, Christ must be both divine and human. And so it is the identity of Christ: pure of soul, infinite of being, and human of substance.