un-be-lef’: The word (the King James Version) represents two Greek words, apeitheia, "disobedience" (only in Ro 11:30,32; Heb 4:6,11), and apistia, "distrust," the antithesis to "faith". (which see). The two words are not only akin etymologically but run into one another by mental connection, certainly where spiritual relations are concerned, as between man and God. For when God has spoken, in precept and yet more in promise, distrust involves, at least potentially, an element of disobedience. His supreme claim is to be trusted to command only what is right, and to promise only what is true. He is infinitely sympathetic in His insight, and infallibly knows where distrust comes only of the dim perceptions and weak mis-givings of our mortal nature, and where, on the other hand, a moral resistance lies at the back of the non-confidence. But the presence of that darker element is always to be suspected, at least, and searched for in serious self-examination.
We may remark that it is a loss in our language that "unbelief" is the only word we can use as the antithesis to "faith"; for "faith" and "belief" (which see) are not exactly synonyms. "Unfaith" would be a welcome word for such use, if it were generally so understood.