Alistair pointed this out to me, and I can't believe I didn't realize it before. Set right down in what is perhaps the hardest passage in all of Romans, Paul makes a statement that God's purposes are only for mercy, and ours are for destruction. Traditionally I had understood this as "I'm fitting vessels for wrath to endure forever, and I'm fitting vessels for mercy to endure forever. But on closer inspection I realized I was importing this bad understanding into the text, not getting it out of it.
I'll put the passive voice in red and the active stuff in green.
"What if God, desiring to show his wrath and to make known his power, has endured with much patience vessels of wrath prepared for destruction, in order to make known the riches of his glory for vessels of mercy, which He has prepared beforehand for glory"What is God doing in the first half of this sentence? He's enduring. He's putting up with. It takes long suffering and much patience and He's waiting them out. And notice what He's not doing, He's not fitting them. That must mean that man fits himself. This is like Pharaoh, who Paul also doesn't forget to mention earlier in the chapter. How did Pharaoh fit himself for destruction? By rejecting the grace of God. By throwing away the second, third, and hundredth chance given to Him. By continually fighting against God.
What is God doing in this verse if He's not fitting the vessels for wrath? Why, preparing the vessels for mercy of course. And how do you prepare someone for mercy? You have them fall and endure their sinfulness. It's the same action, but depending on the will of the person it gives two different results. God outfits everyone for mercy, it's just that the non-elect fit themselves for wrath by rejecting that mercy while the elect God makes to accept it.