Beloved Christian Scientists, keep your minds so filled with Truth and Love, that sin, disease, and death cannot enter them. It is plain that nothing can be added to the mind already full. There is no door through which evil can enter, and no space for evil to fill in a mind filled with goodness. Good thoughts are an impervious armor; clad therewith you are completely shielded from the attacks of error of every sort. And not only yourselves are safe, but all whom your thoughts rest upon are thereby benefited.
The self-seeking pride of the evil thinker injures him when he would harm others. Goodness involuntarily resists evil. The evil thinker is the proud talker and doer. The right thinker abides under the shadow of the Almighty. His thoughts can only reflect peace, good will towards men, health, and holiness.
First Church of Christ and Miscellany, p. 210:2