The system of education in ancient India required the students to live in the campus of a forest academy along with the teachers. The teaching imparted was, almost always, in the form of sutras or aphorisms, followed by explanations and discussions. At a time when committing things to memory was considered supremely important, this method suited admirably.
The sutra literature is a class by itself. As per the norms set for a sutra , it should be alpaksara(consisting of minimum number of letters )asandigdha (with out doubt as regards the meaning ) saravat(must contain the essence of the subject) and ye visva-tomukha (reflect all aspects of the same). However in their anxiety to economise the words, the composers of the sutra-works seem to have so overdone it that bhasyas or explanatory commentaries by later writers became necessary.
The srauta, the grhya and the dhrama sutras form the earliest bunch of sutra literature. The darsanas or the philosophical system which are of a later period, followed this sutra model since it served their purpose well.
A brief study of the Brahma Sutras-- Swami Harshananda.