How can a believer struggle with assurance?

Even true believers may experience struggles with assurance regarding their salvation. This can arise from various factors such as personal doubts, ongoing sin, or feeling distant from God. John acknowledges the reality of this struggle in 1 John 3:19-21, where he speaks of our hearts condemning us, yet reminds us of God's greater assurance. It’s critical for believers to turn their focus away from their performance or feelings and instead rest in Christ’s finished work, understanding that assurance is ultimately based on His faithfulness rather than our fluctuating emotions or actions.