Why is sin a serious matter for Christians?

1 John 3 teaches that 'Whosoever committeth sin transgresseth also the law; for sin is the transgression of the law.' Sin remains a critical issue for Christians because it stands opposed to the righteousness and character of God. While believers are made righteous in Christ, the presence of sin in their lives must not be ignored or taken lightly. Rather, true believers are called to pursue righteousness, as reflecting the nature of Christ results in purification of their hearts. Continuous unrepentant sin may indicate a lack of genuine salvation, urging believers to examine their lives and hold fast to Christ's commandments.