As one advances in meditation, visions like those of mist, smoke, sunlight, fire, breeze, light of firefly, lightning, crystal, moonlight, and so on, are possible. These visions are indicative of spiritual progress. When one masters in meditation the natures belonging to the five elements, earth, water, fire, air and ether, one rises, says the Upanishad, above the torments of illness, old age and even death, on account of his having acquired a flaming spiritual body. Then it is that qualities like lightness of body, perfect health, non-covetousness, resplendence of body, fineness of voice, fragrance of personality, etc. This is said to be the first stage of realisation in Yoga.
Higher stages are further above.
The Yogi, by degrees, unites his soul with Brahman which is unborn, eternal and omnipresent, by knowing which one is freed from all bondage. The soul that is freed from the bonds of world-existence traverses through its physical, vital, mental, intellectual and causal vestments and rejoices in the ecstasy of the realisation of Brahman. Here comes the knowledge that the experiencer, the experiencing process and the experienced object or condition are all one. I have encompassed the whole Universe. In Moksha or liberation all the principles and powers that were confined to individuality get released into their sources or divine essences, which again are merged in Brahman.