Question: Why do you tell us not to let any bad thoughts enter the mind while we are meditating?Sri Chinmoy: During ordinary activity if an evil thought enters into you, you are not so disturbed, since the power of that thought is not very intense. But during meditation if a wrong thought comes, then it is like an arrow entering and piercing your inner life. Indian sadhus say to be very careful during meditation. If silly ideas enter our normal life we don't have to be disturbed. But if they enter during meditation we should try to kill them immediately because the meditation will only intensify them. If you have good thoughts, divine thoughts, during meditation, these same divine and unique qualities will be intensified. Good thoughts, when they enter, are just as intense as bad thoughts, but bad thoughts kill and good thoughts give new life. So at the time of meditation please feel that each divine thought will take you to God and each undivine thought will take you to death.
Sri Chinmoy, The hunger of darkness and the feast of light, part 1, Agni Press, 1974