Calvin on Certainty

I think there's an idea floating around that faith used to mean "complete lack of doubt," and that recent Christian attempts to "reconcile" faith with doubt are just products of modern or existentialist thinking. It makes sense that Kierkegaard would write about the leap of faith (or, in his own terms, the leap to faith) - but would Paul think in the same way?

I'm not going to analyze Paul's writings for existential angst, but I will point out a relatively modern-sounding quotation from John Calvin I recently saw:
"When we inculcate that faith ought to be certain and secure, we conceive not of a certainty attended with no doubt, or of a security interrupted by no anxiety; but we rather affirm, that believers have a perpetual conflict with their own diffidence, and are far from placing their consciences in a placid calm never disturbed by any storms. Yet, on the other hand, we deny, however they may be afflicted, that they ever fall and depart from that certain confidence which they have conceived in the divine mercy."