We proceed to the third article thus:
1. It seems that for salvation it is not necessary to believe anything which is beyond natural reason. For it seems that what naturally belongs to a thing is sufficient for its salvation and perfection. Now the things of faith are beyond natural reason, since they are unseen, as was said in Q.1, Art.4. To believe in them is therefore unnecessary for salvation.
2. Again, it is precarious for a man to give his assent when he cannot judge whether what is proposed to him is true or false. As it is said in Job 12:11: "Doth not the ear try words?" Now a man cannot so judge of the things of faith, because he cannot see how they are derived from their first principles, which is the way in which we judge of all things. To believe such things is therefore precarious, and consequently unnecessary for salvation.
3. Again, according to Ps.37:39: "the salvation of the righteous is of the Lord," man's salvation consists in God. Now it is said in Rom.1:20: "the invisible things of him . . . are clearly seen, being understood by the things that are made, even his eternal power and Godhead." But things which are clearly seen by the intellect are not believed. For salvation, therefore, it is unnecessary to believe anything.
On the other hand: it is said in Heb.11:6: "without faith it is impossible to please him."
I answer: throughout the natural order, two things concur towards the perfection of a lower nature. One of these is its own movement. The other is the movement of a higher nature. Thus water moves towards the centre by its own movement, but moves round the centre, ebbing and flowing, owing to the movement of the moon. The planets, similarly, move from west to east by their own movement, but move from east to west owing to the movement of the first heaven. Now it is only rational created nature that is immediately related to God. Other creatures do not attain to anything universal, but only to what is particular. They share in the divine goodness only in so far as they "are," as in the case of inanimate things; or in so far as they "live, and know singulars," as in the case of plants and animals. But a rational nature is related immediately to the universal principle of all being, in as much as it knows the universal meaning of "good" and of "being." The perfection of a rational creature therefore consists not only in what belongs to it in consequence of its own nature, but also in what it derives from a certain participation in the divine goodness. The ultimate blessedness of man accordingly consists in a supernatural vision of God, as we said in 12ae, Q.3, Art.8. Now a man cannot attain to this vision unless he learns from God who teaches him, according to John 6:45: "Every man therefore that hath heard, and hath learned of the Father, cometh unto me." But he does not become a partaker of this learning all at once. He attains it gradually, according to the mode of his nature. Anyone who learns in this way is bound to believe, if he is to attain to perfect knowledge. Thus even the philosopher observes that "it behoves the learner to believe" (1 Elenchi, ch.2). Hence if a man is to attain to the perfect vision of blessedness, it is essential that he should first believe God, as a learner believes the master who teaches him.
On the first point: man's nature depends on a higher nature. His natural knowledge is consequently insufficient for his perfection, for which something supernatural is required, as we have said.
On the second point: by the natural light of reason, a man assents to first principles. By the habit of a virtue, similarly, a virtuous man rightly judges what is becoming for that virtue. In this same way, by the divinely infused light of faith a man assents to the things of faith, but not to what is contrary to faith. There is therefore nothing precarious in such assent, and no condemnation to them which are in Christ Jesus.
On the third point: in many respects, faith perceives the invisible things of God in a way higher than that of natural reason as it reaches towards God from creatures. Hence it is said in Ecclesiasticus 3:23: "Many things beyond human understanding have been revealed unto thee."