OHC 111.3
(Our High Calling 111.3)
Few realize that it is a duty to exercise control over their thoughts and imaginations. It is difficult to keep the undisciplined mind fixed upon profitable subjects. But if the thoughts are not properly employed, religion cannot flourish in the soul. The mind must be preoccupied with sacred and eternal things, or it will cherish trifling and superficial thoughts. Both the intellectual and the moral powers must be disciplined, and they will strengthen and improve by exercise. (OHC 111.3) MC VC