15.31. On the authority of Sruti (Tai Up 2.4 and 2.9), it is said that words fail to describe the Self. It is also explained on the basis of reason. Words describe an entity if it falls in one of the five categories, namely, species (e.g., tree), property (e.g., colour), action (e.g., servant), relationship (e.g., son) and convention (proper name). The Self does not belong to any of the five categories. This is why verbal description is difficult. All descriptions are from the standpoint of other entities which involves duality. If it is said not small one will think big. The only way to understand the Self is as I am Brahman.
15.32. The nearest entity comparable to the Self is the space. Like space, It is all-pervading and It accommodates everything in the sense that It is their substratum. Yet it is not attached to them. The Self is pure and formless. According to Vedanta, Self-knowledge is the supreme goal.