At the opening of his chapter on "Ango" in SHOBOGENZO, Dogen Zenji refers to a poem by his teacher Zen Master Tendo Nyojo:
Set your bones upright upon level ground,
And to seclude yourself scoop out a cavern in space.
Pass forthwith beyond the gate of dualities,
Only taking with you a darkness as dark as a black lacquered pail.
(Trans. Hubert Nearman, Shasta Abbey)
Dogen Zenji is saying that we are already committed to practice, we've arrived at our place of practice and it's time to settle in to space, where we truly reside. In entering this cavern in space, we live without any interruptions to our lives, we become one-minded and focused purely on practice. We put away all distractions and throw ourselves completely into our training because this summer practice period is one of our important life tools.
Dogen Zenji says that we have already demonstrated our intention to train and we have already learned the methods of practice, nevertheless, we still have our old habits of heavy eating and lounging around when we feel like, so we should waste no time in getting ourselves together for this important retreat. He says that the summer retreat is the very crown of Buddha and that to enter this retreat is to meet the Ancestors. The summer retreat he says is what an Ancestor is. There is only the cavern of space and there is no other earth we can point to.
Another quote from Dogen Zenji on Ango, "Ordinary folk, as well as the saintly, treat the ninety days as a comfortable cave for them to reside in, but these ninety days go far, far beyond the realm of the ordinary and the saintly. These ninety days cannot be reached by thinking about them, nor can they be reached by not thinking about them, nor are they simply something that is unreachable by thinking about or not thinking about them."
So, we enter Ango and find our leisure in the cave of practice. No other outside worries. No worries about trying to think ourselves into the space of practice. Practice cannot be accomplished by thinking, cannot be reached by intellection. We actually have to do it just as the Buddha did and all other Ancestors.
I encourage everyone to make special effort during this time. It's actually a very joyful time and experience to come together with the Sangha to attend to our own spiritual health and confirm our Buddha Nature, realize ourselves as the Three Treasures. Pack up right now and get here. Dig out your space cave and dwell entirely in It.