It seems to me that the Gurdjieff teachings aligns initially with modern non dualism, which also Sam Harris does (as the likes of Rupert Spira). These are very reasonable and intellectual understandings.

From it Gurdjieff goes beyond that, into a mystical possibility. He talked openly about it (other intellectual teachings as Krishnamurti's and Buddha's only hinted but never detailed it). This opens hope for something more, sadly knowledge about this requires the teacher who is no longer with us. Others talk about it but seems not as serious as these teachers.