With him it is not at all what it is to the trained clairvoyant, who ranges through it and lives amidst the surroundings which he finds there, precisely as he would in the physical or astral worlds.

The ordinary man has all through his life been encompassing himself with a mass of thought-forms.

Some which are transitory, to which he pays little attention, have fallen away from him long ago, but those which represent the main interests of his life are always with him, and grow ever stronger and stronger.

If some of these have been selfish, their force pours down into astral matter, and he has exhausted them during his life in the astral world.

But those which are entirely unselfish belong purely to his mental body, and so when he finds himself in the mental world it is through these special thoughts that he is able to appreciate it.
His mental body is by no means fully developed; only those parts of it are really in action to their fullest extent which he has used in this altruistic manner.