While they were thinking, etc. It is commonly inferred from this passage, that Paul alludes here to those philosophers, who assumed to themselves in a peculiar manner the reputation of wisdom; and it is thought that the design of his discourse is to show, that when the superiority of the great is brought down to nothing, the common people would have no reason to suppose that they had any thing worthy of being commended: but they seem to me to have been guided by too slender a reason; for it was not peculiar to the philosophers to suppose themselves wise in the knowledge of God, but it was equally common to all nations, and to all ranks of men. There were indeed none who sought not to form some ideas of the majesty of God, and to make him such a God as they could conceive him to be according to their own reason. This presumption I hold is not learned in the schools, but is innate, and comes with us, so to speak, from the womb. It is indeed evident, that it is an evil which has prevailed in all ages -- that men have allowed themselves every liberty in coining superstitions. The arrogance then which is condemned here is this -- that men sought to be of themselves wise, and to draw God down to a level with their own low condition, when they ought humbly to have given him his own glory. For Paul holds this principle, that none, except through their own fault, are unacquainted with the worship due to God; as though he said, "As they have proudly exalted themselves, they have become infatuated through the righteous judgment of God." There is an obvious reason, which contravenes the interpretation which I reject; for the error of forming an image of God did not originate with the philosophers; but they, by their consent, approved of it as received from others. [1]

Footnotes

1 - Calvin is peculiar in his exposition of this verse. Most critics agree in thinking that those referred to here were those reputed learned among all nations, as Beza says, "Such as the Druids of the Gauls, the soothsayers of the Tuscans, the philosophers of the Greeks, the priests of the Egyptians, the magi of the Persians, the gymnosophists of the Indians, and the Rabbins of the Jews." He considers that the Apostle refers especially to such as these, though he speaks of all men as appearing to themselves very wise in their insane devices as to the worship of God. The wiser they thought themselves, the more foolish they became. See Jeremiah 8:8, 9; 1-Corinthians 1:19-22. "This is the greatest unhappiness of man, not only not to feel his malady, but to extract matter of pride from what ought to be his shame. What they deemed to be their wisdom was truly their folly." -- Haldane. It is a just remark of Hodge, "That the higher the advancement of the nations in refinement and philosophy, the greater, as a general rule, the degradation and folly of their systems of religion." As a proof he mentions the ancient Egyptians, Greeks, and Romans, as compared with the aborigines of America. -- Ed.

Professing themselves to be wise - This was the common boast of the philosophers of antiquity. The very word by which they chose to be called, "philosophers," means literally "lovers of wisdom." That it was their boast that they were wise, is well known; compare Romans 1:14; 1-Corinthians 1:19, 1-Corinthians 1:20, 1-Corinthians 1:22; 1-Corinthians 3:19; 2-Corinthians 11:19.
They became fools - Compare Jeremiah 8:8-9. They became really foolish in their opinions and conduct. There is something particularly pungent and cutting in this remark, and as true as it is pungent. In what way they evinced their folly, Paul proceeds immediately to state. Sinners of all kinds are frequently spoken of as fools in the Scriptures. In the sense in which it is thus used, the word is applied to them as void of understanding or moral sense; as idolaters, and as wicked; Psalm 14:1; Proverbs 26:4; Proverbs 1:17, Proverbs 1:22; Proverbs 14:8-9. The senses in which this word here is applied to the pagan are,
(1) That their speculations and doctrines were senseless; and,
(2) That their conduct was corrupt.

Professing themselves to be wise - This is most strikingly true of all the ancient philosophers, whether Greeks or Romans, as their works, which remain, sufficiently testify. The word φασκοντες signifies not merely the professing but the assumption of the philosophic character. In this sense the word φασκειν is used by the best Greek writers. See Kypke. A dispassionate examination of the doctrine and lives of the most famed philosophers of antiquity, of every nation, will show that they were darkened in their mind and irregular in their conduct. It was from the Christian religion alone that true philosophy and genuine philosophers sprang.

(g) Professing themselves to be wise, they became fools,
(g) Or, thought themselves.

Professing themselves to be wise,.... The learned men among the Gentiles first called themselves "Sophi", wise men: and afterwards, to cover their wretched pride and vanity, "Philosophers", lovers of wisdom; but notwithstanding all their arrogance, their large pretensions to wisdom, and boast of it
they became fools; they appeared to be so; they showed themselves to be such in those very things they prided themselves with the knowledge of: as, for instance, Socrates, after he had asserted the unity of God, and is said to die a martyr for the truth; yet one of the last actions of his life was sacrificing a cock to Aesculapius, at least he desired his friend Crito to do it.

Professing themselves--"boasting," or "pretending to be"
wise, they became fools--"It is the invariable property of error in morals and religion, that men take credit to themselves for it and extol it as wisdom. So the heathen" (1-Corinthians 1:21) [THOLUCK].