4. However, as man must concur in the general progress, and as certain events must result from his cooperation, he can be useful in certain cases if he has a knowledge of these events, in order that he may prepare the way for them, and hold himself ready to act when the right moment comes. That is the reason God permits sometimes a corner of the veil to be lifted; but it is always for a useful object, and never to satisfy a vain curiosity. This mission can then be given not to all spirits; for there are some who know the future no better than men, but to some spirits sufficiently advanced for that. Now, it is well to observe that this kind of revelation is always made spontaneously, and never, or very rarely at least, in response to a direct demand.