Aquinas on the Necessity of the Incarnation - Compendium of Theology 198-201

In these later chapters of Aquinas' Compendium of Theology, he lays out reasons which he thinks thatthe incarnation of Christ as man was fitting and necessary. 

Of course in beginning this discussion, the mention of the Original Sin must be made. Aquinas talks about how Adam and Eve were first in a state of original justice and innocence towards  before they sinned. Now once they did sin, these two states were lost. Adam fell into injustice (guilt before God) and lost that innocence. Now, even if Adam repented from that sin, it would not be enough to undue or fix that sin and restore things to the way they were because that justice before God was a grace given to us, once which we cannot earn by our own works. Thus, everyone born from Adam would receive the fallen state which he brought upon himself from him. 1 

Yet, God is not going to create humanity just to let it completely fall into ruin and fail. God offers a pathway to redemption for Adam in order to undue the damage that his sin has caused. Humans were created for the high calling of beatitude with God, a calling which cannot tolerate any stain of sin within the person sharing that beatitude. Thus, it is fitting that God offer man a way in which he can become clean once again and achieve the high calling which awaits him.  2

Now this is where it gets interesting. Aquinas says that by virtue of divine justice, some recompense must be made for the offense that took place, but God cannot rectify this because to bring satisfaction to an offense there must be one party who is subordinate to the other, and God cannot be subordinate to anything. Man is of course subordinate, but as was mentioned, he does not have the ability to achieve such a high grace as the one given him by his own works and effort. Therefore, are we stuck in a conundrum? 

Well, Aquinas uses this as the reason why God had to become man. In does this, Jesus not only represents human beings, but at the same time represents God as well, having both united in his person. There is divine recompense that is made which restores the wound to divine justice. This is done from the perspective of the hypostatic union with a true human nature, thus humanity is represented in this. A perfect offering to divine justice has been made for us, and therefore all those who are descended by Christ through grace can be restored, just as all those who descended from Adam were tainted. 3

This seems to be at the heart of the argument for why the incarnation was necessary. Now it is not clear from this passage if Aquinas means that the incarnation was absolutely necessary, as if there was no other way of redemption. He only says "hence divine wisdom found it fitting...". Here's the larger context of the quote: 

"But if God had decided to restore man solely by an act of His will and power, the order of divine justice would not have been observed. justice demands satisfaction for sin. But God cannot render satisfaction, just as He cannot merit. Such a service pertains to one who is subject to another. Thus God was not in a position to satisfy for the sin of the whole of human nature; and a mere man was unable to do so, as we have just shown. Hence divine Wisdom judged it fitting that God should become man, so that thus one and the same person would be able both to restore man and to offer satisfaction. This is the reason for the divine Incarnation assigned by the Apostle in 1 Timothy 1:15: 'Christ Jesus came into this world to save sinners.'" 4

Now a few other reasons why Aquinas says the incarnation makes sense logically are: First, the loss of our spiritual grace means that the life of the soul is, in a sense, suppressed by the appetites of the body. Therefore, in God becoming man we once again see the dignity of the body and through that dignity can be lead back to the dignity of our spiritual nature as well. We are embodied spirits and the incarnation allows us to appreciate both aspects of our being. Second, in God becoming man we get a glimpse of the depth of love that God had for us. This shows such an abundance of care and love for human beings that God was willing to humble himself into human form. Bringing us into the third point, that in seeing this depth of love and the possibility of the unity of God and man in Christ, we then are reminded and led toward our ultimate beatitude, to share the same transformed state as Christ had in Heaven. 5

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1 - 198

2 - 199

3 - 200

4 - 200

5 - 201