Aaron Denlinger on John Calvin on Theological Trespassing. I don’t know that the term “trespassing” is helpful – it carries with it the image of someone sitting on his front porch with a shotgun – but the concept is useful.
It’s no sin to ask questions about things which scripture doesn’t clearly answer. But the answer should take the form of, “Maybe X, maybe Y, maybe Z, but scripture doesn’t say.” That’s basically what Paul does in Romans 9:22. It’s helpful to dip your toe in a couple of theological maybes. It expands the imagination and reminds us that God has his reasons, which are perfectly good, whatever they are. But moving from “maybe” to “clearly” generally results in us saying something foolish and insulting about God. My mom always says that all heresy involves taking what is clear in scripture to its obvious conclusion. I have no idea who she’s quoting.