This instruction orients the listener to one of the core characteristics of the awareness space: its lack of boundaries, edges and limits.
Sam Harris
There's no indication of the size or the scope of awareness. There's no edge to your visual field. There's no boundary that defines the energy of your body.
This is an exercise for an experiential recognition of what in Tibetan Buddhism is called "the vast expanse". That is the "ground" aspect, or, as Sam Harris prefers to call it, the "condition" in which every mental event occurs. It is the equivalent of the ocean in the "Ocean and Wave" metaphor.
In Mahamudra teachings, the "vast expanse"
must be experienced and not only conceptually understood
is without limit (the feeling or perception that there are limits is itself just an appearance in limitless awareness)
is without time and change (it doesn't come and go in time, but everything appears in it, as an event)
In this meditation, Sam Harris provides a rudimentary instruction to represent limitlessness by using the inner visual field as an example.
Limitlessness as precondition for enlightenment (Daniel P Brown)
Daniel P Brown explains the systematic reason why limitlessness must be "fully experienced": he sais that it is the basis for the realization of enlightenment.
This a quote from one of Daniel P Brown´s introductions to his translations of Tibetan works:
Pointing out limitlessness serves as the basis for the realisation of enlightenment. In order to fully experience limitlessness, it is important to see if the ordinary mind has imposed any mental constructions of edges or boundaries upon limitless space .
And in the following quote, he explains what must be done in meditation.
If so, the practitioner "opens" (...) his or her awareness directly into any edges or boundaries, like pouring space into space, until the edges dissolve like mist into the atmosphere. The practitioner continues this process until all residual impositions of edges and boundaries disappear and there is a direct experience of genuinely limitless empty awareness/space (Daniel P Brown in intro to Gyaltsen et al., 2022, p 117)
Without this experience, the meditator will also not be able to isolate all events from the background space and to develop a truly non-dual simultaneous view of "the inseparable pair" of ground and events.
Sam Harris´ instruction, in contrast, is pretty simplistic, it is a one-liner.
There is no edge to your visual field.
In another meditation he is more explicit:
Whatever seems like a boundary, whatever seems to impose structure, is itself just an appearance in this condition of awareness.
In Daniel P Brown´s "Pointing Out the Great Way" meditations, the student receives a lot more support to build in the inside experience of infinite, boundless, timeless, changeless space.
As a fully worked out example, here the transformation of the above theoretical text into a pointing out instruction:
Now investigate if this field of knowing awareness-space extends in every direction, like an infinite vast expanse. Boundless. If the ordinary mind imposes any edges and boundaries on this awareness, you can move right into the boundaries and edges with your awareness. When you move into the boundaries with your awareness, they immediately dissolve like mist dissolving into the atmosphere. Keep moving into all the edges and boundaries. It is like pouring space into space, pouring awareness into awareness. If the ordinary mind imposes edges and boundaries somewhere further out, just keep moving into those edges and boundaries with your awareness, until it is perfectly clear to you that this awareness is boundless, edgeless. This field of knowing awareness space is timeless and changeless on one hand, and boundless, edgeless on the other hand, like a vast ocean of changeless, boundless awareness (Pointing Out the Great Way - Retreat Levels, 2022)
In the full meditation, the teacher will repeat the terms "boundless", "limitless" many times during the meditation. This way, the instructions constantly refresh the imagination in a rather hypnotic manner, until the student, by just following the instructions, hopefully gets a convincing experience of limitlessness.
And what about timelessness?
At least during the 9 months I am listening to the meditations, Sam Harris has not integrated timelessness and changelessless as experience into his meditations.
To me this is inexplicable, since having an approximate experience of timelessness helps to represent the space as a "field of awareness which doesn´t change but within which everything else appears".
But maybe this will come in later meditations. Or, Sam Harris considers it as too advanced or difficult. Modifying the felt sense of time may be more difficult that doing that with space.
Resources
Gebel, T. (2022, May 29). Be ocean 1: meditation and contemplative neuroscience. till-gebel.de. https://www.till-gebel.com/post/becoming-ocean-1-meditation-neuroscience
Gebel, Till. (2022b). The inseparable pair (2). Till Gebel. Retrieved 29 September 2022, from https://www.till-gebel.com/post/sam-harris-daily-meditation-2022-09-27-the-inseparable-pair-2-simultaneity
Gyaltsen, S. T. (2022). Self-Arising Three-fold Embodiment of Enlightenment: [of Bon Dzogchen Meditation] (English Edition). In G. S. Gurung & D. P. Brown (Trans.), No Title (2nd ed.). Mustang Bon Foundation. https://www.amazon.com/-/de/dp/1732157944/