In the time between your sleeping and waking — quite unconsciously, of course, as regards the normal consciousness — you will work upon much of what you are now in a position to hear. You will work upon it a great deal in your next sleep and perhaps also during the following nights. One sees souls labouring between sleeping and waking in quite a different fashion at what they have absorbed. And even if it occurred that someone had listened very inattentively, and had merely been somewhat receptive, yet through that receptivity he would draw into his soul the spiritual powers and impulse in the lecture. And that would be worked upon during sleep, and transformed into what we require not only for the rest of life up till death, but beyond death. Thus we work over our whole life as it transpires by day between our waking and sleeping.
Everything we experience by day we work upon during the night. Thus as it were, we learn lessons which we need for all the rest of our life here, and beyond death into the next incarnation. When we are asleep, we are our own prophetic transmuters of our life. This sleep-life is full of tremendously deep riddles, for it is much more deeply connected with what we experience, than is the external consciousness, and we work at it all from the standpoint of its fruitfulness for the following life. What we can make of ourselves through what we have experienced, is the object of our labour in the time between sleeping and waking. Whether we become stronger and more powerful in our soul, or perhaps have to reproach ourselves, we labour at all our experiences so that they become life-fruit. You see from this, that the life between sleeping and waking is really enormously significant, and that it goes deeply into the whole riddle of man.
Source: Rudolf Steiner – GA 157a – The Forming of Destiny and Life after Death:
LECTURE 1: SPIRITUAL LIFE IN THE PHYSICAL WORLD AND LIFE BETWEEN DEATH AND REBIRTH – Berlin, 16th November, 1915
Translated by Harry Collison