But the period beginning with the rise of Greek philosophy and ending with the principate of Claudius will ever remain of the highest interest and importance as showing what human reason, putting forth its highest powers in the race in which it culminated, but at the same time more thoroughly separated from belief, tradition, and authority than anywhere else, did actually achieve. It is in this respect that the heathen philosophers, together with the poets and historians who precede the publication of the Christian religion in the Roman world, possess a value far beyond any intrinsic merit of their own. It is a study of pathology the results of which are far as yet from being gathered in. It is only by carefully examining what the philosophers taught in theology and morals--for they aspired to be and were both the theologians and the moralists of those ages--that we can at all form an adequate judgment of the real work which the Christian Church has wrought in the world. It is only by using the historians and poets as a mirror of that general society to whose cultured classes the philosophers spoke, that we can estimate what the great mass of mankind then was, and what effect the philosophers produced on them. The difference between their world and their society and ours is the measure of Christian work. The hundred years preceding Claudius, which include in them almost all the greatest names of Roman literature, are the most important of all in this point of view, both as containing the result of scientific thought in the five preceding centuries, and as giving the depth of the moral and intellectual descent. We learn from this whole long period the fulness of the truth conveyed in those words of the angelic doctor at the commencement of his great work: "Even for those things which can be investigated concerning God by the force of human reason, it was necessary for man to be instructed by a divine revelation, because few only, and they after long inquiries, and with the admixture of many errors, would convey to man the truth concerning God as searched out by reason."(475)
What the philosophers from the time of Thales had taken as their special work was to measure and estimate the visible world. And for the last four centuries of this period especially they made the nature and the needs, the supreme good and the happiness of man their chief concern, in subordination to which they continued their physical inquiries. And surely the judgment which an inspired writer formed of their travail must recur to the mind with great force at the end of the preceding review: "If they knew so much as to be able to estimate the visible world, why did they not more easily discover its Lord?"(476) Why from the goods which they beheld had they not power to know the sole possessor of being, nor when they gave attention to his works, recognised their artificer? Why did they esteem fire or breath, rapid air or circling stars, or the force of water, or the lights of heaven rulers of the universe? For if the visible beauty of these delighted them so that they conceived them to be gods, how did they not draw the conclusion that the Lord of these was so much better than they? for it was the Author of beauty who created them. If they were struck dumb with the sense of their power and operation, why did they not conceive how much more powerful He who made them was? For from the greatness and the beauty of creatures the parent of them is by the force of reason discerned.(477)