Question: have mercy on whom he will?
Answer: Romans 9:15, NASB: "For He says to Moses, 'I WILL HAVE MERCY ON WHOM I HAVE MERCY, AND I WILL HAVE COMPASSION ON WHOM I HAVE COMPASSION. '" Romans 9:15, NLT: "For God said to Moses, 'I will show mercy to anyone I choose, and I will show compassion to anyone I choose.