No sin, no Incarnation
In order to understand his explanation, it is important to consider what he says earlier in the Question, in Article 3, about the issue of whether God would have become incarnate had the human race not fallen into sin. Aquinas answers in the negative. Though God could have done so, Aquinas says, he would not have. Scripture so emphasizes the theme that the Incarnation occurred as a remedy for sin that the natural conclusion to draw, in Aquinas’s view, is that there would have been no need for it otherwise. Elaborating on the point, Aquinas says that in falling into sin, man “stooped to corporeal things” instead of rising up to God, and that this is what made it fitting for God to become corporeal so as to raise man back up again.
Now, why exactly is this fitting? Yet earlier in the Question, in Article 1, Aquinas emphasizes that “the very nature of God is goodness… [and] it belongs to the essence of goodness to communicate itself to others.” And out of his goodness, says Aquinas, God “did not despise the weakness of His own handiwork.” The idea seems to be that sin has exposed us to the weaknesses entailed by corporeality (from which we would have been protected had our first parents obeyed). To restore us to strength, God in his goodness imparts himself to us by becoming a member of the human race and thereby taking on corporeality.
Exactly how this strengthens us is elaborated on in turn in Article 2, wherein Aquinas makes a number of points. For one thing, the Incarnation aids us in disentangling ourselves from the evil in which we’ve become enmeshed. For that God has taken on our nature and the devil has not helps us to come to prefer the former to the latter. And by underlining the dignity of human nature, the Incarnation prompts us to avoid sullying that nature with further sin. Moreover, Christ’s innocence encourages us away from the sin of presumption, and his humility encourages us away from pride. And of course, his sacrifice on the cross makes satisfaction for our guilt.
For another thing, the Incarnation positively aids us in pursuing what is good, in several ways. By speaking to us directly, as a human being himself, God makes the truths of revelation better known to us, thereby fostering the theological virtue of faith. By taking on our nature he also shows the depth of his love for us, thereby fostering the virtue of hope. Insofar as this prompts us to love God in return, it also fosters in us the virtue of charity. By living a perfect life, Christ sets an example of how we ought to live. By uniting divinity and humanity in himself, he reveals something of the supernatural end of the beatific vision, which also involves such a union (albeit not in exactly the same way).
Not too soon
In these ways, then, the aim of the Incarnation was to remedy the sin into which the human race has fallen. But now Aquinas goes on to argue that to realize this aim, it was best that the Incarnation occurred just when it did, rather than closer to either the beginning or the end of human history.
In Article 5, he proposes several reasons why it was not fitting for the Incarnation to occur soon after the fall of our first parents. First of all, in order for human beings to understand the need for the Incarnation, it was necessary for them to perceive the inadequacy of their natural powers and their desperate need for special divine assistance. And only when “the disease gained strength” was that possible. The idea here is that the dire ramifications and intractability of sin are fully manifest only after many generations have passed.
Second, we tend (by nature, Aquinas seems to be saying) to arrive at perfection only from imperfection, and to understand the spiritual only after understanding the natural. Putting the Incarnation at the beginning of human history rather than later in the story would be contrary to this order of things. Third, with the Incarnation as with the arrival of the merely human dignitaries we are familiar with in everyday experience, it is fitting that the event be preceded by heralds.
Aquinas does not elaborate, but it seems to me that what he is driving at is the need for what is traditionally referred to as the praeparatio evangelica or “preparation for the Gospel.” The Incarnation could not properly be understood just at any old time or location. Rather, the right cultural preconditions had to be in place. Consider that, as St. Paul famously noted, the notion of God incarnate dying on the cross was a stumbling block for the Jews, and seemed foolishness to the Greeks (1 Corinthians 1:23). To be sure, it is not in fact foolishness and should not have been a stumbling block. But there is a sense in which it is precisely because the Jews and many of the Greeks had a proper understanding of the divine that it seemed to be both.
It is clear enough why a Jewish audience of the day would be scandalized by the doctrine. A commitment to God’s unicity and absolute distinctness from the creation had been cemented into the psychology of the people of Israel over the course of centuries, as a long series of prophets and divine punishments gradually purged the nation of any vestige of idolatry. The claim that there are three Persons in the one God, and that one of them took on flesh and died on a cross, was therefore bound to be shocking. But these ideas would not have been properly understood if they were not shocking. If God is one, how can he be tripersonal? If he is the creator of the material world, how could he take on flesh? It was essential that the Jewish people, the first recipients of the Gospel, understood that however these doctrines are to be spelled out, they are not to be interpreted in terms of the idea that the God of Israel is merely part of some pantheon of corporeal deities – as they very easily would have been interpreted had a horror of idolatry not taken deep root among the Jewish people by the first century AD. And inculcating such a horror was part of the point of the establishment of the ancient nation of Israel and the law given through Moses.
Now, the Gentiles too needed a proper conception of the divine nature if they were correctly to understand the central claims of Christianity once it was propagated beyond its original Jewish context. Suppose your understanding of the divine were molded entirely by stories about the gods of Olympus, or by myths about dying deities like Adonis, Attis, Osiris, or Dionysus. Then the Trinity will sound like just another pantheon, the virginal conception of Jesus will be interpreted as comparable to Zeus’s impregnation of various mortal women, and the crucifixion and resurrection of Jesus will be reminiscent of a dying and rising fertility god. In other words, they will seem to be mere variations on familiar pagan themes. However, if instead you conceive of God as the purely actual prime unmoved mover of the world (as in Aristotelianism), or as the non-composite One from which all else derives (as in Neo-Platonism), then the claims of Christianity will sound as shocking as they did to the Jews of the first century. How could that which is pure actuality take on flesh and suffer? How could that which is utterly simple or non-composite be three divine Persons?
Again, these central claims of Christianity, properly understood, are in fact neither scandalous nor foolish. The point, though, is that they are so subtle and difficult – and indeed, they are mysteries in the sense that we could not have learned of them apart from special divine revelation – that a proper initial understanding of them should be jarring. If it were not, that would likely reflect some serious misinterpretation (as the later Christological heresies do).
A last consideration Aquinas gives in Article 5 is that faith and charity tend to wane over time, and indeed it is foretold that they will wane especially in the last days. Hence it was important that the Incarnation not occur too early in human history, lest its benefits become inaccessible too soon. But this brings us to Aquinas’s treatment of the question of why the Incarnation did not occur later in history.
Not too late
In Article 6, Aquinas explains why the Incarnation was not put off until the end of the world (as it might seem it should have been, given the considerations adduced in the previous Article). Once again he makes several points, and the first is, I think, most easily explained in terms of the language of efficient and final causes (though Aquinas himself does not here use those terms). As he said in the previous article, because with human beings imperfection precedes perfection, it was fitting that the perfection of the Incarnation be preceded by the imperfection of human history between the fall of our first parents and the time of Christ. Now, you might think of the Incarnation as the final cause or end toward which that history pointed. And in our experience, the realization of an end or final cause comes later in time than the processes that lead to it.
However, the Incarnation is also an efficient cause of our perfection. And in our experience, efficient causes typically come before their effects (even if, as the metaphysician knows, some efficient causes operate simultaneously with their effects, and God’s causality is altogether atemporal). Hence, in order for us to be able to understand the Incarnation as a final cause, it was fitting that it not occur too early in human history. But in order for us to be able to understand it also as an efficient cause, it was fitting that it not occur too late in human history – that we be able to observe its effects in the foundation of the Church and spreading of the Gospel in the centuries after the time of Christ. (Anyway, this is, again, my own explanation of what Aquinas is getting at in his first point.)
Another point Aquinas makes (his third, actually, but I’ll treat them out of order) is that it is fitting that human beings be saved by faith in something past as well as by faith in something future. He does not elaborate, but I’d propose doing so as follows. Faith involves trusting the testimony of divine authority concerning matters that are usually not otherwise knowable to us. Now, sometimes things are not knowable to us because they are in the future, to which we have no access. But sometimes they are not knowable to us because they are past, and the past is also something to which we have no access, or at least no direct access. Hence, Aquinas seems to be saying, it is fitting that faith involves matters of the latter sort as well as the former sort. And the Incarnation’s being a past event (which it could not have been if it occurred at the end of the world) makes it possible for it to be among the things we know by faith in what God has done in the past. (For those who lived before the Incarnation, of course, it would have been something they would know by faith in what is future.)
The remaining (and in my view more interesting) point made by Aquinas is this. There is a tendency toward decline in human history, such that “men's knowledge of God [begins] to grow dim and their morals lax.” This is why God had to send a succession of prophets to restore things, such as Abraham and Moses – and, finally, Christ, who effected a much greater restoration precisely by virtue of his Incarnation. “But if this remedy had been put off till the end of the world,” Aquinas says, “all knowledge and reverence of God and all uprightness of morals would have been swept away from the earth.”
The idea seems to be that the effects of original sin are so profound that without the Incarnation, even a succession of prophets would provide only temporary respite, and the human race would eventually sink into complete darkness and depravity unprecedented even in the history of the world prior to Christ. As it is, Christian teaching is that a period of such darkness and depravity will indeed occur prior to the end of the world. But it will occur precisely as a result of apostasy from the faith. And Aquinas’s point seems to be that it would have occurred sooner, or would have occurred without the intervening period of illumination provided by Christian teaching, had the Incarnation not happened when it did.
Just how bad things would have been is indicated by another remark Aquinas makes, to the effect that God “came when He knew it was fitting to succor, and when His boons would be welcome.” Perhaps what Aquinas means is that had the Incarnation occurred much later, then the human race would have become so extremely corrupt that the Incarnation would simply not have been accepted. Of course, prophets are typically resisted, but not by everyone, which is why they go on to be revered and their message has an impact at least after their deaths. But the implication of Aquinas’s remarks may be that had the Incarnation been put off too long, human minds and wills would have been so thoroughly corrupted that it would have been of no effect. A chilling thought, that – and also an indicator of how depraved human beings will become in the great apostasy predicted for the last days.