The Katha Upanishad, which we have been studying, was written much later than that to which we now turn — the Chhândogya. The language is more modern, and the thought more organised. In the older Upanishads the language is very archaic, like that of the hymn portion of the Vedas, and one has to wade sometimes through quite a mass of unnecessary things to get at the essential doctrines. The ritualistic literature about which I told you which forms the second division of the Vedas, has left a good deal of its mark upon this old Upanishad, so that more than half of it is still ritualistic. There is, however, one great gain in studying the very old Upanishads. You trace, as it were, the historical growth of spiritual ideas. In the more recent Upanishads, the spiritual ideas have been collected and brought into one place; as in the Bhagavad Gitâ, for instance, which we may, perhaps, look upon as the last of the Upanishads, you do not find any inkling of these ritualistic ideas. The Gita is like a bouquet composed of the beautiful flowers of spiritual truths collected from the Upanishads. But in the Gita you cannot study the rise of the spiritual ideas, you cannot trace them to their source. To do that, as has been pointed out by many, you must study the Vedas.