There's no need to dissect the theological concept of grace. It's more satisfying and joy-inducing when left embedded in the nitty gritty of life.
I do want to point out, however, that this story of grace doesn't give the full picture of what is happening here.
It is portrayed as the story of Jameel, an innocent man, forgiving a person, Andrew, guilty of blatant and malicious harm done to Jameel himself.
A critical aspect of this story is that Jameel is not innocent. He may be innocent of selling drugs, but he isn't innocent. Jameel is guilty of blatant and malicious harm done toward God, and he knows it.
Now, here's the pay-off. Jameel forgives Andrew because he was on the receiving end of grace, God's grace. When we experience the profound grace of God we have the power to show grace to others, even in the messiest of circumstances.
Forgiveness begets forgiveness.
Mercy begets mercy.
Grace begets grace.
At least it should. That's why this story Jesus told is so appalling and disgusting. The benefit of grace demands the expression of it.