Your above quote from Nagarjuna is on the teaching of the subject of non-duality. It is a Mahayana doctrine that there is no ultimate difference between Samsara and Nirvana, defilement and purity, ignorance and enlightenment. Conventional dualities as we understand it is denied, as ultimately all phenomena are empty of all characteristic and that all dharmas have one nature, which is no-nature." I believe one would not find this teaching of non-duality in the Theravada tradition which is aim at the extinction of suffering, i.e. going from the conditioned world of Samsara to the unconditioned Nirvana and not aiming for a unifying principle in our experience of the phenomena world itself.