(21) They knew enough of God to know that thanks and praise were due to Him; but neither of these did they offer. They put aside the natural instinct of adoration, and fell to speculations, which only led them farther and farther from the truth. The new knowledge of which they went in quest proved to be fiction; the old knowledge that they had was obscured and lost by their folly. Starting with two things--a portion of enlightenment on the one hand, and the natural tendency of the human mind to error on the other, the latter prevailed, and the former became eclipsed.

But became vain in their imaginations.--They were frustrated--reached no good and sound result with their speculations.

Their foolish heart.--Not the same word as "fools," in the next verse. Their unintelligent heart; their heart which, by itself, was endowed with no special faculty of discernment such as to enable them to dispense with the enlightenment from above.

Verse 21. - Because that, knowing God, they glorified him not as God, neither were thankful (rather, gave thanks); but became vain in their imaginations (διαλογισμοῖς, elsewhere more correctly rendered "thoughts" or "reasonings;" cf. 1 Corinthians 3:20, "The Lord knoweth the thoughts of the wise, that they are vain" - μάταιοι, as here, ἐματαιώθησαν), and their foolish heart was darkened.

1:18-25 The apostle begins to show that all mankind need the salvation of the gospel, because none could obtain the favour of God, or escape his wrath by their own works. For no man can plead that he has fulfilled all his obligations to God and to his neighbour; nor can any truly say that he has fully acted up to the light afforded him. The sinfulness of man is described as ungodliness against the laws of the first table, and unrighteousness against those of the second. The cause of that sinfulness is holding the truth in unrighteousness. All, more or less, do what they know to be wrong, and omit what they know to be right, so that the plea of ignorance cannot be allowed from any. Our Creator's invisible power and Godhead are so clearly shown in the works he has made, that even idolaters and wicked Gentiles are left without excuse. They foolishly followed idolatry; and rational creatures changed the worship of the glorious Creator, for that of brutes, reptiles, and senseless images. They wandered from God, till all traces of true religion must have been lost, had not the revelation of the gospel prevented it. For whatever may be pretended, as to the sufficiency of man's reason to discover Divine truth and moral obligation, or to govern the practice aright, facts cannot be denied. And these plainly show that men have dishonoured God by the most absurd idolatries and superstitions; and have degraded themselves by the vilest affections and most abominable deeds.Because that when they knew God,.... Though they had such a knowledge of the being and perfections of God, yet

they glorified him not as God. They neither thought nor spoke honourably of him; nor did they ascribe those perfections to him, which belonged to him; they did not adhere to him as the one and only God, nor honour him as the Creator of all things out of nothing, and as the sole Governor of the universe; they did not glorify him by the internal exercise of fear of him, love to him, or trust in him, nor by any external worship suitable to his nature, and their own notions of him, Seneca is an instance of this, of whom Austin (f) says,

"that he worshipped what he found fault with, did what he reproved, and adored that which he blamed.''

Neither were thankful; neither for the knowledge of things they had, which they ascribed to themselves; nor for their mercies, which they imputed to second causes:

but became vain in their imaginations; the vanity or their minds was the spring and source of their evil conduct; which may design the wickedness of their hearts, and the imaginations thereof, which were evil, and that continually; the pride of their natures the carnality and weakness of their reasonings, and the whole system of their vain philosophy; and hence they ran into polytheism, or the worshipping of many gods:

and their foolish heart was darkened; where they thought their great wisdom lay: darkness is natural to the hearts and understandings of all men, which is increased by personal iniquity; Satan is concerned in improving it, and God sometimes gives up the hearts of persons to judicial blindness, which was the case of these men.

(f) De Civitate Dei, l. 6. c. 10.