Meditation is dangerous and unprofitable to the man who enters upon it without the basis of a good character and of clean living. Meditation then becomes only a medium for the bringing in of energies which but serve to stimulate the undesirable aspects of his life, just as the fertilizing of a garden full of weeds will produce a stupendous crop of them, and so crush out the weak and tiny flowers.
Meditation is dangerous where there is wrong motive, such a desire for personal growth and for spiritual powers, for it produces, under these conditions only a strengthening of the shadows in the vale of illusion and brings to full growth the serpent of pride, lurking in the valley of selfish desire. Meditation is dangerous when the desire to serve is lacking.
(Alice Bailey, a Treatise on White Magic)