That is the reason why meditation is necessary in all these things; because without the creative power of thought we cannot organise the body in the world which is nearest to the physical.
Now, supposing that we recognise that our consciousness working in the physical brain, the instrument over which we have complete control, is continually at work contacting the outer world, using the brain as an instrument on which it can play, and continually bringing down from higher worlds impressions which it transmits more or less perfectly to the physical plane, we need not dwell upon our ordinary thinking.
Let us take thinking a little more unusual, where the finer part of the brain, its etheric matter, is being more largely vitalised, more definitely used.

The powers of the imagination--the creative power--the artistic powers, all creative in their nature, these utilise most the ethers of the brain, and, by working in those, bring into activity the lower and coarser matter of the dense brain.

Now, the thought passes from the consciousness through vehicle after vehicle to find its clear expression here.

But do you not have many mental impressions that are not clear, not well defined, and yet which impress you deeply, and of which you feel sure?
They are of many kinds, and reach you in many ways.

What is important to you is simply this for the moment: that being surrounded by the astral and mental worlds, contacts from these are continually touching you, continually causing changes in your consciousness.