How do we know mourning for sin is true repentance?

Mourning for sin is an indicator of true repentance, as it emerges from a conscious awareness of one's sinful nature and the offense it causes to a holy God. In Psalm 51:4, David exemplifies this when he states, 'Against you, you only have I sinned.' This deep sorrow stems from the realization of sin's vileness and the accompanying weight of guilt. It is a sorrow that goes beyond mere regret; it produces a genuine turning away from sin and a seeking of God’s forgiveness. The one who mourns thusly experiences the promise of comfort, as articulated by Jesus.