Mother, by a mental effort -for instance, the resolution not to take medicines when one is ill-can one ,succeed in making the body understand.

That is not enough. A mental resolution is not enough, no. There are subtle reactions in your body which do not obey the mental resolution, it is not enough. Something else is needed.
      Other regions must be contacted. A power higher than the mind's is needed No, it is not in the mental field that the victories are won. It is impossible. It is open to all influences, all contradictory currents. All the mental constructions one makes carry their own contradiction with them. One can try to overrule it or make it as harmless as possible, but it exists, it is there, and at the slightest weakness or lack of vigilance or inadvertance, it enters, and destroys all the work. Mentally, one arrives at very few results, and they are always mixed. Something else is needed. One must pass from the mind into the domain of faith or of a higher consciousness, to be able to act with safety.
     It is quite obvious that one of the most powerful means for acting on the body is faith. People who have a simple heart, not a very complicated mind , simple people, you see -who don't have a very great, very complicated mental development but have a very deep faith, have a great power of action over their bodies, very great. That is why one is quite surprised at times: "Here's a man with a great realisation,an exceptional person, and he is a slave of all the smallest physical things, while this man, well, he is so simple and looks so uncouth, but he has a great faith and goes through difficulties and obstacles like a conqueror!"
     I don't say that a highly cultured man can't have faith, but it is more difficult, for there is always this mental element which contradicts, discusses, tries to understand, which is difficult to convince, which wants proofs. His faith is less pure. It is necessary, then, to pass on to a higher degree in the evolutionary spiral, pass from the mental to the spiritual; then, naturally, faith takes on a quality-of a very high order. But I mean that in daily life, ordinary life, a very simple man who has a very ardent faith can have a mastery over his body- without it being truly a "mastery"; it is simply a spontaneous movement-a control over his body far greater than somebody who has reached a much higher development.

  The Mother