Summa contra Gentiles3.147 Chapter CXLVII. That man needs the divine assistance in order to obtain beatitude

Whereas it is clear from the foregoing, that divine providence governs rational creatures otherwise than other things, inasmuch as they differ from others in natural condition, it remains to be proved that also on account of the excellence of their end, a more exalted mode of government is applied to them by divine providence.

It is evident that in keeping with their nature, they attain to a higher participation of the end. For, since they are of an intellectual nature, they are able by their operation to be in touch with intelligible truth: which is impossible for other things, since they lack intelligence. And, forasmuch as they attain to intelligible truth by their natural operation, it is clear that God provides for them otherwise than for other things: in that to man is given intelligence and reason, that thereby he may be able both to discern and to discover the truth: also to him are given the sensitive powers, both interior and exterior, that by them he may be assisted to discover the truth: also to him is given the use of speech, so that by making use of it, one who has conceived the truth in his mind, may be able to impart it to another: so that men may thus assist one another in the knowledge of truth, even as in other necessaries of life, since man is by nature a social animal.

Furthermore, the knowledge of truth that is appointed as man’s last end is one which surpasses his natural faculty: for it consists in his seeing the First Truth itself in itself, as we have proved above. Now this is not competent to lower creatures, namely that they be able to reach an end surpassing their natural faculty. Consequently, there arises from this end an additional reason why a different manner of government should be accorded to men, and to other creatures of a lower nature. Because the means should be proportionate to the end. So that, if man be directed to an end surpassing his natural faculty, he stands in need of a supernatural assistance from God, to enable him to tend to that end.

Moreover. A thing of inferior nature cannot attain to what is proper to a higher nature except by virtue of that higher nature: thus the moon, that shines not of itself, is made to shine by the power and action of the sun: and water that is not hot of itself, becomes hot by the power and action of fire. Now, to see the First Truth itself in itself, so far surpasses the faculty of human nature, that it belongs to God alone, as we have shown above. Therefore man needs the divine assistance in order to reach that end.

Again. Everything obtains its last end by its own operation. Now, an operation derives its efficacy from the operating principle: wherefore by the action of the seed something is produced in a definite species, through the efficacy pre-existing in the seed. Therefore man cannot, by his own operation, attain to his last end, which surpasses the faculty of his natural powers, unless his operation be enabled by the divine power to bring him thereto.

Besides. No instrument can achieve ultimate perfection by virtue of its own form, but only by virtue of the principal agent: although by virtue of its own form it can cause some disposition to the ultimate perfection. Thus a saw, by reason of its own form, causes the cutting of the wood, but the form of the bench is produced by the art that employs the instrument: likewise in the body of an animal, resolution and consumption is the result of the animal heat, but the formation of flesh, and regulation of increase and other such things, come from the vegetative soul, which uses heat as its instrument. Now, to God the first agent by intellect and will, all intellects and wills are subordinate, as instruments under the principal agent. Consequently their operations have no efficacy in respect of their ultimate perfection, which is the attainment of final beatitude, except by the power of God. Therefore the rational nature needs the divine assistance in order to obtain its last end.

Further. Many obstacles prevent man from reaching his end. For he is hindered by the weakness of his reason, which is easily drawn into error which bars him from the straight road that leads to his end. He is also hindered by the passions of the sensitive faculty, and by the affections whereby he is drawn to sensible and inferior things, since the more he adheres to them, the further is he removed from his last end: for such things are below man, whereas his end is above him. Again he is often hindered by weakness of the body from doing acts of virtue, whereby he tends to beatitude. Therefore he needs the help of God, lest by such obstacles he turn away utterly from his last end.

Hence it is said (Jo. vi. 44): No man can come to Me, unless the Father, who hath sent Me, draw him: and (xv. 4): As the branch cannot bear fruit of itself, unless it abide in the vine, so neither can you, unless you abide in Me. Hereby we refute the error of the Pelagians, who asserted that man can merit the glory of God by his free-will alone.