"container" in this context refers back to Charlotte Joko Beck who in Everyday Zen spoke about the ABC of practice — A Bigger Container.I looked for extracts and found this one from anmolmehta.com/blog
We can talk about 'oneness' until the cows come home. But how do we actually separate ourselves from others? How? The pride out of which anger is born is what separates us. And the solution is a practice in which we experience this separating emotion as a definite body state. When we do, A Bigger Container is created.A search for "Bigger Container" on the "look Inside" feature of Amazon's page for Everyday Zen lets you read the entire "A Bigger Container" chapter (pp 49 - 52) from which this extract is drawn.
What is created, what grows, is the amount of life I can hold without it upsetting me, dominating me. At first this space is quite restricted, then it’s a bit bigger, and then it’s bigger still. It need never cease to grow. And the enlightened state is that enormous and compassionate space. And how do we know where this cut-off point is? We are at that point when we feel any degree of upset, of anger. It’s no mystery at all. And the strength of our practice is how big that container gets.
This practice of making A Bigger Container is essentially spiritual because it is essentially nothing at all. A Bigger Container isn’t a thing; awareness is not a thing; the witness is not a thing or a person. There is not somebody witnessing. Nevertheless that which can witness my mind and body must be other than my mind and body. If I can observe my mind and body in an angry state, who is this 'I' who observes? It shows me that I am other than my anger, bigger than my anger, and this knowledge enables me to build A Bigger Container, to grow. So what must be increased is the ability to observe. What we observe is always secondary. It isn’t important that we are upset; what is important is the ability to observe the upset.
As the ability grows first to observe, and second to experience, two factors simultaneously increase: wisdom, the ability to see life as it is (not the way I want it to be) and compassion, the natural action which comes from seeing life as it is. We can’t have compassion for anyone or anything if our encounter with them is ensnarled in pride and anger; it’s impossible. Compassion grows as we create A Bigger Container.