Romans 5:21, according to the King James Version of the Bible, states, "That as sin hath reigned unto death, even so might grace reign through righteousness unto eternal life by Jesus Christ our Lord." This verse serves as the conclusion to the larger passage in Romans 5:12-21 which focuses on the contrast and comparisons between Adam's sin and Jesus Christ's sacrifice and the resulting effects on humanity.

The verse starts by emphasizing the lasting impact of sin, stating that 'sin hath reigned unto death.' This highlights the destructive power of sin and its ability to bring about spiritual and physical death. In the preceding verses, the Apostle Paul outlines how sin entered the world through Adam and as a result, all of humanity is affected by sin, leading to our spiritual separation from God and eventual physical death.

However, the latter part of Romans 5:21 offers a glimmer of hope by introducing the concept of grace. The verse states that 'even so might grace reign through righteousness unto eternal life.' This suggests that just as sin has had a controlling influence over humanity, grace can also have a controlling influence, but bringing forth righteousness and leading to eternal life. This speaks to the transformative power of grace, which offers salvation and eternal life through Jesus Christ.

The verse concludes by attributing this grace and righteousness to Jesus Christ, stating, 'by Jesus Christ our Lord.' This reinforces the belief that salvation and eternal life are only made possible through the redemptive work of Jesus Christ. This provides a clear message of hope and salvation for all who believe in Him.

In the larger context of the book of Romans, this passage reflects the central theme of Paul's letter, which focuses on the righteousness of God and the salvation offered through Jesus Christ. Throughout the book, Paul emphasizes the universal sinfulness of humanity and the subsequent need for salvation. This verse serves as a poignant conclusion to Paul's argument, highlighting the victory of grace over sin and the assurance of eternal life through Jesus Christ.

The verse also holds significant theological implications, particularly in relation to the doctrine of original sin. The concept of sin reigning unto death through Adam's transgression and the subsequent reign of grace through Jesus Christ is foundational to Christian soteriology. This verse points to the power and sufficiency of Jesus' atoning sacrifice and its ability to overcome the effects of sin and death.

Moreover, the verse introduces the idea of grace reigning through righteousness, emphasizing the transformative power of God's grace to bring about a righteous life. This underscores the believer's ongoing journey of sanctification, as the grace of God continuously works in the life of the believer, leading them towards righteousness and eternal life.

Symbolically, this verse represents the triumph of grace over sin, and the victory of life over death. It serves as a reminder of the hope and assurance that is found in Jesus Christ, offering believers the promise of eternal life and restoration in the righteousness of God.

In conclusion, Romans 5:21 encapsulates the core themes of sin, grace, righteousness, and eternal life within the larger theological framework of the book of Romans. It offers a message of hope and salvation, underscoring the power of grace through Jesus Christ to overcome sin and bring about eternal life for all who believe. It serves as a profound declaration of the transformative and redemptive work of God, providing comfort and assurance to believers.