The Law of Three and Law of Seven are among the most insightful teachings by Gurdjieff (and later P. D. Ouspensky, see In Search of the Miraculous and The Fourth Way).
Together with the Law of Three it gives rise to the Enneagram which in turn lines up with the 8 Rasas found in Rajanaka Abhinavagupta’s commentary on the Natya Shastra (the Abhinavabharati)