Charles Ellicott Commentary Romans 9:15

"For he saith to Moses, I will have mercy on whom I have mercy, and I will have compassion on whom I have compassion." — Romans 9:15 (ASV)

For he says to Moses.—In the most characteristic period of the Old Testament the divine favor was promised in this way to Moses and denied to Pharaoh. The original of the first quotation refers to the special revelation granted to Moses on Sinai, I will show grace to whom I will show grace.