What is the Gospel of Grace?

Tim Keller's Book on Psalms, "My Rock My Refuge", Ps 69:7-12, says:

"The world does not understand this gospel of grace in which holy living is the result of humble, grateful joy, not a way to earn heaven... by living lives of humility, forgiveness, and sacrificial service to others."

There is no need for us to earn our way to heaven because we are already registered there.

• (Philippians 3:20-21 (NLT) 20 But we are citizens of heaven, where the Lord Jesus Christ lives. And we are eagerly waiting for him to return as our Savior. 21 He will take our weak mortal bodies and change them into glorious bodies like his own, using the same power with which he will bring everything under his control.)

But we are to live out this new life of humility, grateful joy, forgiveness, and services to others because:

• 2 Cor 5:20 NLV So we are Christ’s ambassadors; God is making his appeal through us. We speak for Christ when we plead, “Come back to God!
• 2 Corinthians 3:3 NLV You show that you are a (living) letter from Christ,... written not with ink but with the Spirit of the living God, not on tablets of stone but on tablets of human hearts