What Is concrete thinking?

If spirits can move themselves by the power of thought, then it follows that they should also be able to send their thoughts by themselves—unhindered by all ideas of distance. When they focus their thoughts upon some person in the spirit world, whether they be in the form of a definite message—or whether they are solely of an affectionate nature, those thoughts will reach their destination without fail and they will be taken up by the percipient. Although they can thus send their thoughts, it must not be assumed that their minds are as an open book for all to read. 

Spirits can if they so will deliberately keep their thoughts to themselves, but if they should think idly, as it were—if they should just let their thoughts ramble along under loose control, then they can be seen and read by others.

One of the first things to be done upon arrival here is to realise that thought is concrete, that it can create and build, and then your next effort is to place your own thoughts under proper and adequate control. But like so much else in the spirit world, you can soon learn to adjust yourself to the new conditions if you have a mind to do so, and you will never lack the most willing helpers in any—or all of your difficulties.