As a lamp does not flicker in a windless place, i.e., does not move, but remains steady with its illumination—this is the simile used to illustrate the nature of the self of the Yogin who has subdued his mind, who has got rid of all other kinds of mental activity and who is practising Yoga concerning the self. The meaning is that the self remains with its steadily illumining light of knowledge because all other activities of the mind have ceased, just as a lamp kept in a windless place has an unflickering flame.