What is the purpose of so many Upanishads when they all say the same thing?
There are little differences amongst each. Though they all say the same thing, yet the style is very unique and it is not the same thing.
Each one has its own specific flavour. It is like when you go to an ice cream shop and ask, ‘Why have you kept so many flavours of ice cream?’ So, basically they are ice cream but each is a different flavour. One is chocolate, one is pistachio, another is butterscotch, etc. Essentially it is all sugar and cream. The ingredients are essentially the same, but each has a different flavour.