Rudolf Steiner: "In the morning there are to be found in the etheric body, firstly thoughts which have approached it from the environment, and secondly thoughts also which the Masters or other individualities have implanted into it. The introduction of these latter is made possible by the person in question meditating. In that someone occupies himself during the daytime with pure, noble thoughts dealing with eternal things, he brings into his astral body the disposition for such thoughts. Should he not have this disposition, it would be useless were a Master to wish to work upon his etheric body. If one reads Light on the Path and meditates upon it, one prepares the astral body in such a way that when the Master imbues the etheric body with lofty thoughts, the astral body can actually contact them. This is called the relationship of man to his higher self. Such is the true nature of this process. The higher self of man does not live within us, but around us. The more highly developed individualities are the higher self. Man must be clear that the higher self is outside him. Were he to seek for it within himself, he would never find it. He must seek it with those who have already trodden the path that we wish to tread. Within us is nothing except our karma, what we have already experienced in earlier incarnations. Everything else is outside us. The higher self is around us. If, in preparation for the future, we wish to approach it more closely, we must seek it above all in the company of those individualities who can work during the night on our etheric body. The higher self is in the universe; therefore the Vedantist says: ‘Tat twam asi’ — That art thou. If through appropriate writings, such as Light on the Path or the Gospel of St. John, we incline the astral body to take in lofty spiritual nourishment and thus to understand the Masters, we are thereby working in a good way toward what will lead to the higher self. In the night therefore we find in astral space the sleeping bodies, or the pupils with their Masters, insofar as someone who has formed a tie which unites him with the Master, through an appropriate meditation, is led toward him. This is what can happen during the night. It is possible for everyone by immersing himself in inspired writings to reach the point of taking part in such intercourse and through this to attain to the development of his higher self. What in the course of some thousands of years will become our self is now the higher self. In order however really to get to know the higher self we must seek for it where it already is today, with the higher individualities. This is the communication of the pupils with the Masters."
Related post: http://martyrion.blogspot.com/2016/04/devachan-spiritland-tat-tvam-asi-that.html