Recently I've found myself doing more brahmavihara meditation in general, with a particular focus on self-compassion (often appearing as compassion for my parts). On my last retreat, I was surprised to find that this seemed to open up the possibility of some of the immaterial jhanas. It also seemed to lead to an increasing ... blankness ... of experience, as if all the knots that made up the world of phenomena were gradually coming untied. All this was pretty vague however, so I decided to pick up another of Bikkhu Analayo's books, one which promised to somehow connect compassion and emptiness.
Unlike his book on the Satipatthana Sutta, this one is not intended for beginners. Here, Analayo feels free to talk about things like the brahmaviharas and the jhanas without explaining them first. The reader is presumed to be fairly well versed in these concepts at the outset. Also presumed is an at least passing familiarity with early buddhist suttas, though since the book is structured as an in-depth examination of the instructions given in the Karajakaya, Culasunnata, and Mahasunnata suttas, Analayo provides an appendix with his own translations of these.
The basic trajectory Analayo suggests is summed up well by the final chapter entitled Practical Instructions -- 1) use the radiative form of the brahmaviharas as a concentration object to 2) access some level of the first three immaterial jhanas, then 3) proceed from the perception of nothingness to let go of the idea that there is any subject perceiving any thing at all, and 4) finally incline the mind towards Nirvana. While Analayo does not use the term, the penultimate step in this sequence, called the "signless concentration of mind", seems to be a form of nondual perception. Sense data continues but is no longer assembled into objects; life continues, but no longer belongs to a subject, even a subject experiencing 'its' absence of self. Analayo ultimately claims that even this nondual experience somehow falls short of the perfect liberation of Nirvana, though in the end its not clear to me what the difference would be beyond the conceptual category error that arises when we discuss the problem (Nirvana is not a state).
Needless to say, this is the very short version, and the book contains a wealth of more subtle guidance. Just to give an example, one point that will stick with me is the way the connection between compassion and emptiness actually comes about through the boundless and radiating aspect of the brahmaviharas. This form of practice links the tangibility of something like compassion to the abstractions of the sphere of infinite space, consciousness and nothingness. But I think Analayo suggests this approach not just because boundless radiation prepares one for the leap to boundless space and consciousness, but also because it grounds our deeper meditative experiences in a moral practice. So perhaps what we're trying to create here is some sort of ethico-meditative feedback loop where our goodwill towards the world lets us experience deeper internal states, and these deeper internal states in turn allow us to continue extending the circumference of our goodwill. And indeed, meditation does seem to work in just the way this model would imply -- it's not that bad feelings are permanently removed or avoided, but simply that, with practice, good states and good intentions become more numerous and more powerful. The change does not come from some third party perspective outside the system, but from a snowballing cultivation that operates from within.