Romans 1:21 in the King James Version (KJV) of the Bible reads, "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."

This verse is a part of the letter written by the Apostle Paul to the Romans, and it addresses the spiritual condition of those who have turned away from God. In this verse, Paul is describing the state of humanity before their repentance and salvation through Jesus Christ, and he is highlighting the consequences of rejecting the knowledge of God.

The verse begins with the phrase "Because that, when they knew God," which implies that the people being referred to were not ignorant of God's existence or characteristics. They had a basic understanding of who God was and what he required of them, but they chose to disregard and neglect this knowledge. This willful ignorance and disobedience are what led them to the state of spiritual darkness and separation from God.

The next part of the verse states, "they glorified him not as God, neither were thankful." This is the crux of the issue – instead of acknowledging God as the ultimate authority and source of all things, these individuals failed to give him the honor and gratitude that he rightfully deserves. They were ungrateful for the blessings and provisions that God had given them, and they failed to recognize his sovereignty and divine attributes. This lack of reverence and thankfulness set them on a path of spiritual decline.

The verse continues, "but became vain in their imaginations." The word "vain" in this context means empty, futile, or devoid of truth. Their thoughts and desires became centered on themselves and their own selfish ambitions, rather than on the things of God. Their imaginations were filled with pride, self-centeredness, and worldly pursuits, leading them away from the truth and wisdom of God.

Finally, the verse concludes with the statement, "and their foolish heart was darkened." This is a powerful metaphor for the spiritual blindness and hardness of heart that comes as a result of rejecting God. Their inner being, the very core of their being, became clouded with ignorance, foolishness, and sin, leaving them in a state of moral and spiritual darkness.

The themes present in this verse are numerous and profound. It speaks to the consequences of rejecting God and the downward spiral that occurs when we turn away from his truth and goodness. It emphasizes the importance of acknowledging and honoring God as the ultimate authority and source of all things, and the necessity of gratitude and humility in our relationship with him. The verse also highlights the dangers of pride, self-centeredness, and worldly desires, which can lead us astray from God's will and purpose for our lives.

In terms of context, this verse is part of the larger passage in Romans 1 where Paul is addressing the state of humanity and their need for redemption through Jesus Christ. He is building a case for the universal sinfulness of mankind and the need for a Savior to reconcile us to God. This verse serves as a powerful indictment of the human condition apart from God, highlighting the spiritual consequences of rejecting God and the downward spiral that occurs when we turn away from his truth and goodness.

Symbolically, this verse is rich with imagery and meaning. The darkness of the heart represents the spiritual blindness and separation from God that comes as a result of sin. The vain imaginations and foolishness point to the distorted and self-centered mindset that leads us away from the truth of God. And the failure to glorify and be thankful to God represents the ultimate act of rebellion and ingratitude that separates us from our Creator.

In conclusion, Romans 1:21 is a poignant and sobering reminder of the consequences of rejecting God and the downward spiral that occurs when we turn away from his truth and goodness. It serves as a call to humility, gratitude, and reverence for God, and a warning against the dangers of pride, self-centeredness, and worldly pursuits. Ultimately, it points to the need for salvation through Jesus Christ, who offers redemption and reconciliation to all who turn to him in faith.