There are several different levels of knowing.

1. Not knowing
2. Knowing through faith
3. Knowing through witnessing
4. Knowing through experience

This is best explained with an illustration.

Supposing there is a magical fruit that when eaten gives one the greatest pleasurable sensation one can ever experience. And suppose that this knowledge is known only to a limited few. Thus the majority of people do not know about it (Not Knowing).

Let us then suppose that there is a teacher who not only knows about it but possessed the fruit as well and a student came to him to ask him about it. The teacher told him all about the magical fruit and the magical qualities of the fruit and how pleasurable the sensation is for one who has taken a bite of it, but he does not show him the fruit nor offer the student to taste it. That student knows only through faith in the teacher