(For reference, this is from a response to a fellow Calvinist who felt agonized by his wife's barrenness, the thriving of the ungodly, etc., and the to-him-fact that God had directly decreed all this. To the point that his prayer frequency had lessened. The tone of the letter suggested he was imploring Cheung for a way to divine good out of all this so the agony would stop. If you somehow want to read the whole thing, start from p. 100.)

The question that Paul says we should not ask [in Romans 9] is precisely the one that you are asking: "Shall what is formed say to him who formed it, 'Why did you make me like this?'" If you are a reprobate, then the matter is simple. This passage says that God has made someone like you so that someone like me can learn about his wrath, his power, and his patience – that he would tolerate someone like you for so long – and in contrast, about his riches and mercy toward me. So if you are a reprobate, this would be a satisfying conclusion to my response.

However, our working assumption is that you are a Christian. Even so, the passage is relevant. Notice that God reveals himself to the elect not only through the objects of wrath, whom he has prepared for destruction, but those who are saved are objects of his mercy – they themselves have been sinners, only that God has decided to sovereignly show them mercy. "Therefore God has mercy on whom he wants to have mercy, and he hardens whom he wants to harden" (Romans 9:18).