Every command of God comes with a promise. God never commands you to do something He hasn't already empowered you to accomplish.
See to it that no one comes short of the grace of God; that no root of bitterness springing up causes trouble, and by it many be defiled. - Hebrews 12:15
You can't travel through life without experiencing hurt or disappointment. People are going to let you down, and you will make decisions you regret.
If you aren't careful, those hurts and disappointments can take hold in your heart. Unforgiveness always leads to bitterness. This verse describes bitterness as the root of a plant growing deep into your heart. Once that root of bitterness takes hold, it grows and flourishes.
When you don't deal with bitterness, it always causes trouble. How many unhappy, bitter people do you know who have never dealt with hurt or disappointment in their past?
You remove the root of bitterness through forgiveness. For most of us, that is easier said than done. Only through the grace of God can you truly forgive others and yourself. It was God's grace that forgave all your sin. It was his grace that brought restoration to your soul. Through His grace in you, you can forgive others for the hurt they have caused and forgive yourself for the mistakes you have made. Sometimes, the hardest person to forgive is yourself. To release this true forgiveness, you need the grace of God He has already provided.
