Showing undeserved kindness imitates God's character. It's in the Bible, Luke 6:35, TLB. "Love your enemies! Do good to them! Lend to them! And don't be concerned about the fact that they won't repay. Then your reward from heaven will be very great, and you will truly be acting as sons of God: for He is kind to the unthankful and to those who are very wicked."
Genuine kindness is our response to God's love. It's in the Bible, Romans 12:14, TLB. "If someone mistreats you because you are a Christian, don't curse him; pray that God will bless him. When others are happy, be happy with them. If they are sad, share their sorrow."
Kindness is one of the characteristics of God's people. It's in the Bible, Colossians 3:12, NIV. "Therefore, as God's chosen people, holy and dearly loved, clothe yourselves with compassion, kindness, humility, gentleness and patience."