The reason why Sufism is a science of experience, which cannot be read it books... And we are speaking about the fruits of the path.... The best analogy that I can give you, is how do you explain color to a blind person??? You can't, it is something they have to experience to appreciate... So when the sufis speak of secret knowledge it is only secret in the sense, that only those who experience will understand it, if you are unable to experience it, then it will remain a secret until you are able to experience it... And Allah knows best.