Can you be sure?

From what I've read, in the history of philosophy the quest for certainty extends back at least as far as Plato. For Plato, as I understand him, the physical world is not an object of knowledge because the physical world undergoes constant change, which means the object of knowledge is in a state of perpetual flux. For Plato, the object of knowledge is abstract archetypes. 

This had counterparts in Indian philosophy. Take the stock example of whether a coiled object is a snake or a rope. In a land with a superabundance of kraits, cobras, and vipers, that question is of more than academic interest!  

Augustine baptized Plato by relocating archetypes in God's mind. Divine ideas.

Aquinas was more of an empiricist. Ockham was more skeptical regarding the fortunes of religious knowledge. 

Descartes renewed the quest for certainty, with austere results. Some Counter-Reformation apologists revived Pyrrhonian skepticism to deploy against Protestant theology, but that backfired. John Locke and Bishop Butler shifted to probability arguments.  

Is the quest for certainty a mirage? If you combine a Reformed doctrine of providence, which you subscribe to, with a reliabilist theory of knowledge (like Plantinga's proper function account), then special providence is a trustworthy belief-forming process. Of course, reliabilism is disputed, but every thing in philosophy is disputed. One objection to reliabilism is the Cartesian demon, but every epistemology is prey to that artificial thought-experiment.

It's necessary to distinguish between what we know and what we can prove. It may well be the case that no apologetic method can yield absolute certainty. That's due to the fact that not everything we know is reducible to proof. We know more than we can prove. 

There's a difference between certainty in terms of knowledge and certainty in terms of proof. Formal arguments suffer from that limitation.

I can recognize someone's voice on the phone. I couldn't begin to present a rigorous philosophical justification for my recognition. Not everything we know is susceptible to stringent analysis.

That said, I'd like to reframe the debate. In general, that's not how I assess Christianity. I don't begin with whether we can achieve certainty regarding the claims of faith. I think that's a worthwhile discussion, but it sucks up too much oxygen. 

Another approach is to look at the competition. And the competition isn't that impressive. I don't think it's hard to dispose of naturalism. That leaves religious options. The major religious options are Judaism, Islam, Hinduism, Buddhism (although that's technically atheistic), neopaganism, and Taoism–along with some cults (e.g. Mormonism). In a sense, Judaism is a serious contender, but Christianity incorporates Judaism. Likewise, Christianity incorporates the "truth" of paganism (i.e. witchcraft) into its own worldview. What's evil and diabolical can still be true. 

My point is not to make the case here and now. My point, though, is that if by process of elimination, Christianity is the last man standing, then it's pretty irrelevant to ask whether it's a sure thing. If that's the only viable option, then whether or not it's a sure thing is beside the point.

To take a comparison, suppose I'm on the 40th floor of a skyscraper that's on fire. Suppose my floor has four doors leading to emergency exits. I try each door, but three of the four doors are locked. Suppose I'm unsure if the unlocked door leads to an emergency exit. What if I'm misremembering? What if I mistook it for another door? But if all the other candidates are locked, then my level of certainty is irrelevant. Even if they did lead to an emergency exit, they're not live options. The remaining door, the unlocked door, is the only viable choice. Even if it doesn't lead to an emergency exit, I'm not going to stand there, with flames licking at my heels, while I calculate the probabilities. 

Likewise, if the ship is sinking and there's one lifeboat left, I'll jump into the lifeboat. I won't sink under the waves debating whether the lifeboat is seaworthy. By default, that's what I'm left with.