Isaiah 1:18 - "Come now, and let us reason together," says the LORD, "though your sins are like scarlet, they shall be as white as snow; though they are red like crimson, they shall be as wool."
We are to reason with the Lord, to deal with Him, and let Him deal with us. He gives us the promise, even as He calls us to confess, that He will forgive us if we are willing and obedient. You will know your repentance as you are willing to repent before the Lord, as you are willing to offer it to others you have wronged, and as you desire to act differently.
Assurance of Forgiveness – As you have confessed sincerely to God, know that your Father in heaven isn’t angry at you waiting for you to get your repentance right. He is instead loving you as a father, and teaching you how to live a more godly life. As an ambassador of Christ, authorized to speak in his name, I declare to you your sins are forgiven through Christ.