"Forgive one another, as God in Christ forgave you." - Col 3.13
John Piper intimates that our root motive for being a forgiving person is that "God forgave us in such a way that infinite joy in his fellowship becomes ours. God is the goal of forgiveness. He is also the ground and the means of forgiveness. It comes from Him; it was accomplished through His Son; and it leads people back to Him with their sins cast into the deepest sea. Therefore the motive for being a forgiving person is the joy of being freely and joyfully at home with God. At great cost to Himself God gave us what we needed above all things: Himself for our enjoyment forever. God's forgiveness is important for one reason: It gives us God!"
Piper contends that if God is most glorified in us when we are most satisfied in Him, then living for the glory of God must mean that we live to gladly make others glad in God.
When we forgive, we must be clear that it is not for our benefit. It is not so we can avoid hell. It is not so God can hear our prayers. It is so that we can attain God, to be satisfied in Him, and thereby glorify Him. And by forgiving others, we afford them this same opportunity, that they might attain God, be satisfied in Him, and to in turn bring Him glory. Our personal benefit is a side issue, it's just one of the cool things He does. To glorify God is all ultimately matters.
Piper again, "To make others glad in God with an everlasting gladness, our lives must show that He is more precious than life ... Psa 63.3 ... To do this we must make sacrificial life choices rooted in the assurance that magnifying Christ through generosity and mercy is more satisfying than selfishness. If we walk away from risk [God directed risk for the glory of the Kingdom] to keep ourselves safe and solvent, we will waste our lives."