God's purpose declared to Pharaoh
Paul quotes God's words about displaying His power and proclaiming His name through Pharaoh.
For the Scripture says to Pharaoh: “I raised you up for this very purpose, that I might display My power in you, and that My name might be proclaimed in all the earth.” Therefore God has mercy on whom He wants to have mercy, and He hardens whom He wants to harden.
Exodus 9:16 states why God raised Pharaoh up. Romans 9:17 introduces the same words with, "For the Scripture says to Pharaoh."