Vedanta is the end or gist of the Vedas. It deals with the knowledge portion. Vedanta is not mere speculation. It is the authentic record of transcendental experiences or direct and actual realisation of the great Hindu Rishis or seers. Brahma Sutras is the Science of the Soul.
Sutras are concise aphorisms.
They give the essence of the arguments on a topic. Maximum of thought is compressed or condensed into these Sutras in as few words as possible. It is easy to remember them. Great intellectual people only, with realisation, can compose Sutras. They are clues or aids to memory.