How do we know that we cannot lose our salvation?

The assurance of salvation for believers is anchored in the completed work of Christ rather than in the fluctuating holiness of the believer. Romans 8 highlights that those who are in Christ Jesus have been justified and thus cannot be condemned. Since Christ fulfilled the law and took upon Himself the punishment for sin, God will not impose that punishment again on those for whom Christ died. Therefore, salvation is secure because it does not depend on human effort or merit but entirely on God's grace and Christ's righteousness.