Ajahn Brahmavamso on Anatta

 “Bāhiya, you should train yourself thus: in the seen will be merely what is seen, ... in the cognized will merely be what is cognized. Practising in this way, Bāhiya, you will not be 'because of that'. When you are not 'because of that', you will not be 'in that'. And when you are not 'in that', you will be neither here nor beyond nor in between the two. Just this is the end of suffering."

What does it mean "you will not be 'because of that'"? The Pāli is na tena. Tena is the instrumental of the word for 'that'. Na is the negative. It means, literally, "not because of that, not through that, not by that". It means in essence, you will not assume that there is a self, a soul, a me; because of, through, or by; the seen or the heard or the sensed or the cognized. The Buddha is saying that once you have penetrated the truth of sensory experience, by suppressing the Hindrances through Jhāna, you will see that there is no 'doer', nor a 'knower', behind sensory experience. No longer will you be able to use sensory experience as evidence for a self. Descartes' famous "I am because I think" is refuted. You will not be because of thinking, nor because of seeing, hearing or sensing. In the Buddha's words, "You will not be because of that (any sensory experience)".

When the sensory processes are discarded as tenable evidence for a self, a soul or a me, then you are no longer located in the sensory experience. In the Buddha's words, "You will not be 'in that'". You no longer view, perceive or even think that there is a 'me' involved in life. In the words of the doctor in the original series of Star Trek, "It is life, Jim, but not as we know it"! There is no longer any sense of self, or soul, at the centre of experience. You are no more 'in that'.

Just to close off the loophole that you might think you can escape non-existence of a self or soul by identifying with a transcendental state of being beyond what is seen, heard, sensed or cognized, the Buddha thunders, "and you will be neither here (with the seen, heard, sensed or cognized) nor beyond (outside of the seen, heard, sensed or cognized) nor in between the two (neither of the world nor beyond the world). The last phrase comprehensively confounded the sophists!

In summary, the Buddha advised both Bāhiya and Venerable Mālunkyaputta to experience the Jhānas to suppress the Five Hindrances. Thereby one will discern with certainty the absence of a self or a soul behind the sensory process. Consequently, sensory experience will never again be taken as evidence of a 'knower' or a 'doer': such that you will never imagine a self or a soul at the centre of experience, nor beyond, nor anywhere else. Bāhiya's Teaching put in a nutshell the way to the realization of No-Self, Anattā. "Just this", concluded the Buddha "is the end of suffering".” – Ajahn Brahmavamso, https://www.dhammatalks.net/Books6/Ajahn_Brahm_BAHIYA_S_TEACHING.htm , also, he explained anatta from 56 minutes onwards in this video (prior to 56 minutes mark, the explanation focuses on cultivating samadhi): https://youtu.be/RYbe7W7XRu8