If I'm accepted in Christ, why do good?

Yesterday I got to see Tullian Tchvidjian preach at Southern Seminary. I love his focus on the gospel of grace. Toward the end of his message he asked an interesting question: If Christ accepts me based on his righteousness and not mine, then what is my motivation to do good? In other words, if I have a great day, I'm accepted, if I have a bad day, I'm accepted. So why do good? He answered the question with a quote from Spurgeon:

When I thought God was hard, I found it easy to sin; but when I found God so kind, so good, so overflowing with compassion, I smote upon my breast to think that I could ever have rebelled against One who loved me so, and sought my good.

In other words, the deeper I go into the gospel, the greater my motivation toward obedience. I encourage you to watch this message and be amazed again at God's grace for desperate sinners like you and me.