A god and a demon went to learn about the Self from a great sage. They studied with him for a long time. At last the sage told them, ‘You yourselves are the Being you are seeking.’
Both of them thought that their bodies were the Self. They went back to their people quite satisfied and said, ‘We have learned everything that was to be learned; eat, drink, and be merry; we are the Self; there is nothing beyond us.’
The nature of the demon was ignorant, clouded; so he never inquired any further, but was perfectly contented with the idea that he was God, that by the Self was meant the body.
The god had a purer nature. He at first committed the mistake of thinking: I, this body, am Brahman: so keep it strong and in health, and well dressed, and give it all sorts of enjoyments. But, in a few days, he found out that that could not be the meaning of the sage, their master; there must be something higher.
So he came back and said, ‘Sir, did you teach me that this body was the Self? If so, I see all bodies die; the Self cannot die.’
The sage said, ‘Find it out; thou art That.’
Then the god thought that the vital forces which work the body were what the sage meant. But, after a time, he found that if he ate, these vital forces remained strong, but, if he starved, they became weak.
The god then went back to the sage and said, ‘Sir, do you mean that the vital forces are the Self?’
The sage said, ‘Find out for yourself; thou art That.’
The god returned home once more, thinking that it was the mind, perhaps, that was the Self. But in a short while he saw that thoughts were so various, now good, again bad; the mind was too changeable to be the Self.
He went back to the sage and said, ‘Sir, I do not think that the mind is the Self; did you mean that?’
‘No,’ replied the sage, ‘thou art That; find out for yourself.’
The god went home, and at last found that he was the Self, beyond all thought, one without birth or death, whom the sword cannot pierce or the fire burn, whom the air cannot dry or the water melt, the beginningless and endless, the immovable, the intangible, the omniscient, the omnipotent Being; that It was neither the body nor the mind, but beyond them all. So he was satisfied; but the poor demon did not get the truth, owing to his fondness for the body.
This world has a good many of these demonic natures, but there are some gods too. If one proposes to teach any science to increase the power of sense-enjoyment, one finds multitudes ready for it. If one undertakes to show the supreme goal, one finds few to listen to him. Very few have the power to grasp the higher, fewer still the patience to attain to it. (CW, 1:140-42)
Source: The Complete Works of Swami Vivekananda/Volume 1/Raja-Yoga/The First Steps