1. King David was kind to Mephibosheth because he made an agreement with Jonathan, Mephibosheth's father, not because of Mephibosheth's own behavior, and had nothing to do with Mephibosheth's own behavior. But Mephibosheth didn't have an agreement between his father and David. Instead, he came to David with a humble face, such as no pedicure, no shaving and no washing clothes, to please David's heart.
2. God is kind to us, calling us righteous, being heirs with Christ, and getting the eternal inheritance of the kingdom of heaven. It is not because of our kindness and good deeds that we become righteous, but because of the Covenant made by the precious blood of the cross of Jesus.
Hebrews 1:14 Because he sacrificed once, he made the sanctified one perfect forever.
But Satan deceives us, making us forget that we are all evil. He doesn't let us walk to God with the promise of the blood of Jesus' cross. Instead, he always lets us walk to God with our goodness and good deeds to please God, just as Mephibosheth did before David.
Thank God for his grace, which has been guiding us through words, so that we can keep the standard of all evil, accept grace and give all glory to God.