Sleep is indispensable in the present state of the body. It is by a progressive control over the subconscient that the sleep can become more and more conscious.
The Mother – Words of the Mother – III : CWM, Vol. 15, p. 131
Mother, what is sleep? Is it only the need of the body to rest or is it something else?
Sleep can be a very active means of concentration and inner knowledge. Sleep is the school one has to go through, if one knows how to learn his lesson there, so that the inner being may be independent of the physical form, conscious in itself and master of its own life. There are entire parts of the being which need this immobility and semi-consciousness of the outer being, of the body, in order to be able to live their own life, independently.
The Mother – Questions and Answers : CWM, Vol. 7, p. 70