First of all, we should note that being a disciple, or apprentice, of Jesus is a quite definite and obvious kind of thing. To make a mystery of it is to misunderstand it. There is no good reason why people should ever be in doubt as to whether they themselves are his students or not. And the evidence will always be quite clear as to whether any other individual is his student, though we may be in no position to collect that evidence and rarely would have any legitimate occasion to gather or use it.