The great idea of holiness that has been attached to these books has preserved them, more than any other book in the world, from mutilation. In them, thoughts at their highest and at their lowest have all been preserved, the essential and the non-essential, the most ennobling teachings and the simplest matters of detail stand side by side; for nobody has dared to touch them. Commentators came and tried to smooth them down and to bring out wonderful new ideas from the old things; they tried to find spiritual ideas in even the most ordinary statements, but the texts remained, and as such, they are the most wonderful historical study. We all know that in the scriptures of every religion changes were made to suit the growing spirituality of later times; one word was changed here and another put in there, and so on. This, probably, has not been done with the Vedic literature, or if ever done, it is almost imperceptible. So we have this great advantage, we are able to study thoughts in their original significance, to note how they developed, how from materialistic ideas finer and finer spiritual ideas are evolved, until they attained their greatest height in the Vedanta. Descriptions of some of the old manners and customs are also there, but they do not appear much in the Upanishads. The language used is peculiar, terse, mnemonic.