Why I am telling drbrumley that is because he asked me a question about man's ability, or lack of, to thwart God's will. See his post and question
here.
What I mean by it is this: man can no more thwart God's will than a lump of clay could thwart a potter's will.
Rom 9:21
Hath not the potter power over the clay, of the same lump to make one vessel unto honour, and another unto dishonour?
Ok, so how does that verse show man cannot thwart God's will.
1 This is the word that came to Jeremiah from the LORD : 2 "Go down to the potter's house, and there I will give you my message." 3 So I went down to the potter's house, and I saw him working at the wheel. 4 But the pot he was shaping from the clay was marred in his hands; so the potter formed it into another pot, shaping it as seemed best to him.
Jeremiah 18:1-4
Paul wrote the book of Romans. Paul was a pharisee. He knew the old testament. In Romans 9 it tells us that God hardened Pharaohs heart.
17For 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."[g] 18Therefore God has mercy on whom he wants to have mercy, and he hardens whom he wants to harden.
Romans 9:17-18
God has the power to do what he wants with people, but he will not mess with your free will. In the verse from Jeremiah we see that the potters pot was already marred and so the potter formed it into another pot.
Paul was referring to this verse in Jeremiah when writing Romans 9 and by looking at that we can realize that Pharaoh used free will to turn away from God, and when God saw that Pharaoh was already marred he was able to use Pharaoh for the good of Israel by hardening his heart with the plagues. In this same way, we can thwart God's will, and when we do God can still find a way to use us. Your use of Romans 9:21 does not prove anything. It simply promotes the opposite view