What is the purpose in the Gnostic belief “Know Thyself”?
Until you know yourself you will be seeing the world through the prisms of judgment, through veils of perception heaped upon you by parents, teachers, culture, etc, which are not you but have got inside you and feel like you. So you have to sort it all out and find “you”. Once you know yourself you will see the world much more nearly for what it really is. This takes a long time, so by then you will be so old and disgusted with humanity (having seen them for what they are) you are ready to move on to the next level of the game.