I'm really blogging this for myself, so I can refer back to it often.
The things we think on are the things that feed our souls. If we think on pure and lovely things, we shall grow pure and lovely like them; and the converse is equally true. Very few people at all realize this, and consequently there is a great deal of carelessness, even with careful people, in regard to their thoughts. They guard their words and actions with the utmost care, but their thoughts, which, after all, are the very spring and root of everything in character and life, they neglect entirely. So long as it is not put into spoken words, it seems of no consequence at all what goes on within the mind. No one hears or knows, and therefore they imagine that the vagrant thoughts that come and go as they list, do not harm. Such persons are very careless as to the food offered to their thoughts, and accept haphazardly, without discrimination, anything that comes.
Every thought we think, in every hour we live, must be, not necessarily about Christ, but it must be the thought Christ would think were He placed in our circumstances and subject to our conditions. This is what it means really to feed on Him and be nourished by the true bread of life that cometh down from heaven.