Complex sentence: Blavatsky was the leading theoretician of the Theosophical Society, and the ideas expounded in her published texts provide the basis from which the Society and wider Theosophical movement emerged.
Split into simpler sentences: Blavatsky was the leading theoretician of the Theosophical Society, responsible for establishing its "doctrinal basis". The ideas expounded in her published texts provide the basis from which the Society and wider Theosophical movement emerged.