For everyday working purposes, most of us make no distinction between knowing that something is the case and believing that it is. They are interchangeable cognitive goods. They are badges of pride and safety, and sometimes they are taken as signs of who we are. Certainly throughout most of history, one could be denied participation in social life or even killed for seeing the world differently from those in power.
Priests and philosophers served a useful function in the past as guides to good mental hygiene. Not so much anymore.
Don’t blame the scientists. Knowing that the world was a clockwork, deterministic, completely knowable world was largely abandoned a century ago. It is the philosophers who pulled the plug in the bathtub we thought was filled with factual truth. We have had more than a hundred years of demonstrations of what are known as indeterminacy proofs. Einstein’s relativity of mass and space; quantum mechanics that insists that what is fundamentally physical depends on how it is measured; Godel’s mathematically proof that our number system is either consistent or complete (but never both at the same time); Arrow’s proof that agreement on what is socially most desirable is an insoluble problem are examples of the general Turing and Church proof that we cannot know that we know everything. It will hardly do to defend religious certainly by questioning scientific certainty. Knowing that one is right as a foundation for action and judging others is out the window – everywhere. “A is wrong so B must be right” is pretty sketchy logic.
Knowing is associated with certainty, truth, characteristics of the world that are independent of the knower, unchangeable, beyond argument, rational. Knowing is the ultimate and absolute justification for action, even though knowing something is true has no motivating power to cause action.
Believing is associated with faith, willingness to act, expectations about what will come, ever growing and enriching.
Claiming certain knowledge is an illusion. Often it is a sign that our belief is inadequate or a dense against comparing our beliefs with those of others. Sometimes the translation is “I am prepared to stop talking with you because I believe there is no point in continuing the conversation. However, to protect myself from opposing your belief with mine I will say that you are objectively wrong. That means I have access to a more pure and certain source of information than you do.”
Belief is an act of faith. It says, “I am willing to act a certain way.” Knowing that you are right is difficult to get across, so we usually say that others are wrong. That is a conversation stopper and not much of a foundation for building relationships.