I pray these verses will help someone understand that no matter how big we think our sin is, God is always just and faithful to forgive us our sins and cleanse us from all unrighteousness.
Isaiah 1: 18-19 " 'Come now and let us reason
together', says the Lord. 'Though your sins
are like scarlet, they shall be white as snow; though they are red like crimson, they shall be wool. If you are willing and obedient, you shall eat the good of the land.' "
2 Corinthians 5:17 "Therefore if anyone is in Christ, he is a new creation; old things have passed away. Behold, all things have become new."
2 Corinthians 5:21 "For He made Him who know no sin to be sin for us, that we may become the righteousness of God."