Why do Christians struggle with sin?

The struggle with sin is an intrinsic part of the Christian experience, as evidenced by the Apostle Paul's writings in Romans 7. Paul illustrates the inner conflict between the new nature created in Christ and the old sinful nature that continues to exist within believers. This duality leads to a constant battle where the new man delights in God's law while the flesh wars against it, leading to feelings of wretchedness and a longing for deliverance. The assurance for believers is found in Christ, who has redeemed them, and thus they can turn to Him for strength and hope while battling their sins.