What does the Bible say about sinning after salvation?

In John 5:14, Christ admonishes a healed man to 'sin no more, lest a worse thing come upon thee.' This statement highlights the seriousness of sin in the life of a believer. While believers are eternally secure in Christ, sin can disrupt fellowship with God and quench the Holy Spirit. The struggle against sin is real and ongoing, as articulated by Paul in Romans 7, where he speaks about the conflict within between the desire to do good and the reality of sin present in him. Thus, it's crucial for Christians to strive for holiness, not as a means to earn salvation but as a reflection of their transformed nature in Christ.