The three sections do not continue one another and were probably not composed together. The first is concerned with speech: the joining of sounds, the correct pronunciation of the recitation, meditations on the elements of language, and then, abruptly, the address given to a student who has finished his study. The second sets out the self as covered by a series of sheaths, from the one made of food outward through breath, mind and understanding to the one made of bliss, and attempts to measure bliss by multiplying a unit of human happiness through ranks of beings. The third tells a story.
The story is the best of the three. Bhrigu asks his father to teach him the absolute and is told to find it by austerity. He returns saying it is food, is sent back, returns saying breath, is sent back, and so on through mind and understanding until he arrives at bliss. The father never supplies the answer, only the method. Read together the sections move from the outward and technical to the inward and personal, and the tradition treats that progression as intentional, a curriculum in which correct speech comes before analysis of the self and analysis before the discovery a student makes for himself. Whether the sections were arranged to produce that effect or simply accumulated in that order is a separate question, and nothing in the text answers it. What is clear is that the arrangement has been read as meaningful for a very long time.