What does Romans 9:17 mean?

Paul continues to make the case that God is not unjust or "unfair" for choosing to give His mercy to one person and not another. He has offered two examples from Scripture so far. In the first case, God chose to give the covenant promises only to Abraham's son by Sarah and not the children of his other wives. Next, Paul showed that God chose Jacob over Esau while the twin boys were still in their mother's womb, having done nothing right or wrong to earn God's favor or rejection.

Those examples involve an "active" sense of God's mercy. He is not obligated to be merciful to anyone, so there is nothing unjust about God selecting only some to benefit from His grace. If grace was earned, it would not be grace (Romans 4:2–5; 11:6).

Now Paul references the Pharaoh of Israel's liberation from Egypt, with a quote from Exodus 9:16. This comes from God's words to Moses about what to say to Pharaoh before sending another plague. God wanted Pharaoh to know that He had raised Pharaoh—or Egypt—to power and prominence so that God could show His own, much greater, power in bringing Egypt to her knees. God's stated reason for doing this was that His own name would be proclaimed in all the earth.

In other words, God raised up Pharaoh and brought Pharaoh down for the sake of His own glory. This is meant to be understood in the context of Paul's upcoming remarks about a potter having the right to mold clay for his own purposes (Romans 9:20).