Earlier quoted context omitted.
Unless God actually exists and revealed himself to them. Obviously, you are free to not believe that, but believing that goes along with believing what you are dismissing.
He revealed himself to them and only them, ignoring the rest of humanity all over the globe. In all the universe he chose just earth for his people, and over all of earth, he just chose a tiny section to reveal himself to. Omniscient and omnipotent but a very human scale for his messaging.
Faith is a concept, like so many other concepts. It is a unique creation that has properties, one of them is that it’s not meant to be provable that easily.