When you read
Romans 9:17-18: Well, you have to realize it is making a parallel. For there is a parallel being made of how God is Sovereign and just in setting up the Promised Line of the Messiah (i.e. by having mercy on whom He wills) versus raising up Pharaoh into power to show God's power. How was God's power shown in the life of the Pharoah? Well, God allowed Pharoah to be raised up so that God's power was shown in the life of God's miracles being displayed such as the Ten plagues and the parting of the Red Sea. This is why Pharoah was raised up. It was so that God's power (or miracles) could be displayed (and proclaimed to all the Earth). Just as God had chosen the line of the Messiah so as to display His power (and proclaim such a thing to all the Earth). So this was not some kind of point to prove individual election but to prove the Election of the Promised Line of the Messiah (Who is Jesus Christ). For Jesus is the greatest miracle (of the best form of Election) that there is.
Anyways, when you read on down to verse 24 (
Romans 9:24), the point is clear what Paul is really talking about.