No man should allow his mind to be a vehicle for others to use; he who does not direct his own mind lacks mastery.

Our minds need to be dusted and swept just as much as our houses, and this we do by meditation and concentration, which wipe away all wrong impressions. We must be masters of our own minds as well as our houses, and not allow them to be like a furniture warehouse with all the furniture mixed up together. We must direct where everything is to be placed, so that complete order may reign therein.
The more the mind is allowed to go on without purpose, the more likely it is to become a vehicle or machine, which all manner of influences around it of other human beings or spirit obsessions will employ instead of its owner. If the user of that mind is a sensible person, then it may perhaps act properly, but otherwise the work of the mind is wasted. In any case it would not be a fulfillment of the purpose of his life. This purpose is to learn mastery, not to be a vehicle for others to use. He who does not direct his own mind lacks mastery. ...
Man is his mind, is the product of his mind, and is also the controller of the activity of mind. If he does not control his mind, he is not a master but a slave. It lies with his own mind whether he shall be master, or whether he shall be slave. He is slave when he neglects to be master; he is master if he cares to be master. ... A man with a perfectly stilled, comforted, and rested mind will at once raise up another who is going through distress, or restlessness, or pain, or ill-temper, or worry, or anxiety. The very presence of one whose mind is stilled gives such hope, such inspiration, such sympathy, such power and life. All the heavenly properties flow so smoothly and freely from the person whose mind is stilled that his words, his voice, his presence, all react upon the mind of others; and as he stills his mind, so his very presence becomes healing.