How do we know that believers cannot fall away?

The assurance of a believer's perseverance is rooted in the love of God and the work of Christ. As Romans 8:38-39 asserts, nothing can separate us from the love of God in Christ Jesus. This divine protection assures that those whom God has chosen and redeemed are secure in their salvation. Despite the ongoing struggle against sin—the old man within—believers are ultimately upheld by God's grace and remain steadfast in His love, distinguishing them from the non-elect who are left to their own devices.