When a thought is expressed in speech, the vibration of the sound has a considerable power to bring the most material substance into contact with the thought, thus giving it a concrete and effective reality. That is why one must never speak ill of people or things or say things which go against the progress of the divine realisation in the world. This is an absolute general rule. And yet it has one exception. You should not criticise anything unless at the same time you have the conscious power and active will to dissolve or transform the movements or things you criticise. For this conscious power and active will have the capacity of infusing Matter with the possibility to react and refuse the bad vibration and ultimately to correct it so that it becomes impossible for it to go on expressing itself on the physical plane.
This can be done without risk or danger only by one who moves in the gnostic realms and possesses in his mental faculties the light of the spirit and the power of the truth.
He, the divine worker, is free from all preference and all attachment; he has broken down the limits of his ego and is now only a perfectly pure and impersonal instrument of the supramental action upon earth.
Ref : On Education