Great and honorable acts are a great good. This is relevant because, for a holy entity like God Almighty to grant forgiveness to his persecutors, like Paul, is a great and honorable act.1
John 15:13 -- “Greater love has no one than this, that one lay down his life for his friends.”There is also something to be said about the individual who is granting forgiveness here. For the President of the United States to lay down his life for a random person who has attacked him feels as if it is a greater act than a normal sacrifice for two reasons: (a) he is the President, and (b) he is doing it despite the attack. Unlike in the case of the President, God is truly greater than any human, and so God's humbling himself for a mere undeserving man makes God's act far more honorable.
A true evil-conquering story is a great good. This is relevant because the ability for God to turn the greatest evil into the greatest good is arguably the greatest evil conquering story.1
Andy Rau: “God took the very worst thing that has ever happened in the history of the universe — deicide, or the death of God on the cross — and turned it into the very best thing that has happened in the history of the Universe: the opening up of heaven to all who follow Him.” [Why Does God Allow Tragedy and Suffering?]It has long been noted that God can masterfully turn evil into good, and that this is quintessentially displayed on the cross.
Genesis 50:20 -- “As for you, you meant evil against me, but God meant it for good in order to bring about this present result,”
Love-bonds forged in suffering are a great good (especially in the context of eternity).1 This is relevant because Jesus's (God's) forgiveness of such individuals as Paul results in a uniquely special relationship which is otherwise impossible to attain.
Luke 7:47 -- “but he who is forgiven little, loves little”