"As sure as God made little apples" is an asseveration—that is, "a positive or earnest avowal or affirmation"—that dates back more than a century. Since at least the 1800s, it's been the phrase to use to suggest something certain, or intended to be so.

But certain though it may be that God made little apples, that affirmation is not the only phrase of certainty to invoke divine powers, nor is it the only one to refer to food. Authoritative folks of faith who are also fond of alliteration may assert, "As sure as God's in Gloucestershire" when they want to convey conviction. And people with a more rational bent—who are also willing to bend the rules of grammar a bit—have been known to say, "As sure as eggs is eggs." Why do we associate the ungrammatical "eggs is eggs" with reason? Because of a theory (as yet unproven) that "as sure as eggs is eggs" is a corruption of the logician's formula "x is x."