Because that, when they knew God, they glorified him not as God, neither were thankful; but became vain in their imaginations, and their foolish heart was darkened.
when.
Romans 1:19,28 Because that which may be known of God is manifest in them; for God hath shewed it unto them…
John 3:19 And this is the condemnation, that light is come into the world, and men loved darkness rather than light, because their deeds were evil.
they glorified.
Romans 15:9 And that the Gentiles might glorify God for his mercy; as it is written, For this cause I will confess to thee among the Gentiles, and sing unto thy name.
Psalm 50:23 Whoso offereth praise glorifieth me: and to him that ordereth his conversation aright will I shew the salvation of God.
Psalm 86:9 All nations whom thou hast made shall come and worship before thee, O Lord; and shall glorify thy name.
but became.
Genesis 6:5 And GOD saw that the wickedness of man was great in the earth, and that every imagination of the thoughts of his heart was only evil continually.
Genesis 8:21 And the LORD smelled a sweet savour; and the LORD said in his heart, I will not again curse the ground any more for man's sake; for the imagination of man's heart is evil from his youth; neither will I again smite any more every thing living, as I have done.
2 Kings 17:15 And they rejected his statutes, and his covenant that he made with their fathers, and his testimonies which he testified against them; and they followed vanity, and became vain, and went after the heathen that were round about them, concerning whom the LORD had charged them, that they should not do like them.
their foolish.
Romans 11:10 Let their eyes be darkened, that they may not see, and bow down their back alway.
Deuteronomy 28:29 And thou shalt grope at noonday, as the blind gropeth in darkness, and thou shalt not prosper in thy ways: and thou shalt be only oppressed and spoiled evermore, and no man shall save thee.
Isaiah 60:2 For, behold, the darkness shall cover the earth, and gross darkness the people: but the LORD shall arise upon thee, and his glory shall be seen upon thee.
they neither glorified Him as God
The failure to glorify God points to a lack of reverence and worship due to Him. This is a central theme in Scripture, where God demands and deserves glory (Isaiah 42:8). Theologically, this reflects the sin of idolatry, where people turn to created things rather than the Creator (Exodus 20:3-5). This failure is a rejection of God's rightful place in their lives.
nor gave thanks to Him
Ingratitude towards God is a significant issue, as thanksgiving is a fundamental response to His provision and grace (1 Thessalonians 5:18). This lack of thankfulness is indicative of a heart that does not recognize God's sovereignty and goodness. Culturally, this reflects a self-centered worldview, prevalent in societies that prioritize human achievement over divine providence.
but they became futile in their thinking
Futility in thinking refers to the emptiness and vanity of human reasoning apart from God (Ecclesiastes 1:2). This futility is a result of rejecting divine truth, leading to moral and intellectual decay. Biblically, this is seen in the wisdom of the world being foolishness to God (1 Corinthians 3:19). It highlights the contrast between human wisdom and divine revelation.
and darkened in their foolish hearts
A darkened heart signifies spiritual blindness and moral corruption (Ephesians 4:18). This darkness is a consequence of turning away from the light of God's truth (John 3:19-20). Theologically, it represents the state of humanity under sin, unable to perceive or accept spiritual realities without divine intervention. This darkness is overcome only through the light of Christ (John 8:12).
“Although they knew God” (Romans 1:21) points to a genuine, inescapable knowledge granted to every person.
• Creation makes His attributes “clearly seen” (Romans 1:19-20).
• Day and night proclaim His glory (Psalm 19:1-4).
• He “has not left Himself without testimony” in doing good and providing for all (Acts 14:17).
Knowing about God is not merely possible; it is reality. Yet knowledge alone does not equal relationship or worship.
Glorifying God means treating Him as the supreme, weighty reality He is.
• God insists, “I will not give My glory to another” (Isaiah 42:8).
• The heavenly cry eternally declares, “Holy, holy, holy” (Revelation 4:8-11).
• When people fail to honor Him, the result is idolatry—trading the truth for a lie (Romans 1:23-25).
Failing to glorify God is the first outward sign that inward rebellion is underway.
A thankless heart is a proud heart, refusing to acknowledge dependence on the Creator.
• “Give thanks to the LORD, for He is good” frames the worship of Israel (Psalm 136:1-3).
• Ingratitude is a last-days marker of ungodliness (2 Timothy 3:1-2).
• Genuine faith overflows with gratitude: “Whatever you do…do it all in the name of the Lord Jesus, giving thanks” (Colossians 3:17).
Thanklessness hardens the soul and chokes worship at its root.
When God is pushed out, the mind loses true direction.
• “The fool says in his heart, ‘There is no God’” (Psalm 14:1); folly begins where God is dismissed.
• God “frustrates the plans of the peoples” who refuse Him (Psalm 33:10).
• Ephesians 4:17-18 describes the Gentiles as “futile in their thinking…alienated from the life of God.”
Futility means empty conclusions, circular reasoning, and goals that cannot satisfy.
Light rejected becomes darkness within.
• “The path of the wicked is like deep darkness” (Proverbs 4:19).
• Jesus said, “If your light is darkness, how great is that darkness!” (Matthew 6:23).
• Persistent unbelief leads to God giving people over to further darkness (Romans 1:24, 26, 28).
The heart that should perceive God’s glory instead grows dim, incapable of discerning good from evil.
Romans 1:21 traces the tragic slide from awareness of God to deep spiritual darkness. People possess real knowledge of Him, yet when they refuse to glorify and thank Him, their minds empty out and their hearts darken. The verse warns that neglecting worship and gratitude is never neutral; it breeds intellectual futility and moral blindness. Recognizing His glory and giving thanks keep the mind clear and the heart bright in His light.
(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.