Listen to Gaofeng Yuanmiao, a Chan [Zen] master who lived from 1238-1295 AD, from Chan Whip: Breaking Through the Barrier:

This matter [i.e., the Great Matter of Birth and Death, also known as the Great Matter of Life and Death–AT] demands that the practitioners have urgency. Only if you have urgency will the real Doubt arise. Struggle with it, doubting away without even the intention to doubt, day and night. Sticking the head and tail together, your practice becomes constant and without a crack. Shake it – it does not move; chase it – it does not go away. Bright and clear, you are always in it. This is when the practice is working. Be certain to work with the correct mindset and not separate from it! Do it until you walk not knowing you are walking and sit not knowing you are sitting. Cold, heat, hunger or thirst – you know nothing of that. When you get there, it is not far from home! Hitting it or poking it – it is but a matter of time. However, now that you have heard this, don’t go and apply your energy single-mindedly to look for it; don’t sit around waiting for it to happen; nor should you just let it be or drop it!

You misunderstand meditation, at least as it’s practiced in Rinzai Zen, if you think it’s about calming down and “cooling your jets.” It’s not! It’s not that at all! If anything, it’s just the opposite!

There’s no genuine point in sitting if you haven’t been existentially opened. Sans existential opening, it’s just a cute thing to do. It’s nice to fart around and cross your legs and close your eyes and, well, make believe. But that’s not meditation.

True meditation begins when the Great Matter of Life and Death is in your face, in your bones, rattling your lungs. Only now, as the Buddha and Dogen knew, does the “noble search” begin.

And sure enough, if you’re earnest and fierce, that life-question–that koan–ripens. It just happens! Sure, sometimes it’s “tasteless” in the mouth, but really it’s a slow, or fast, turning up of the temperature to the point at which you can barely bear it.

See how the situation is impossible? Isn’t this what Gaofeng Yuanmiao is getting at?

1. You can’t go looking for enlightenment “single-mindedly” because doing so tries to make what you seek into an object, a discrete ‘something.’ Yet it is not that. Can’t be that.
2. BUT you also can’t wait around for it. Remember the impending mortality? The mortality that you can feel in your bones? The Great Mystery of being and non-being?
3. And the key, so simple yet also so forceful, is that you can’t leave it alone! You can’t let the koan drop!

The koan demands a breakthrough! Nothing less will do! And “grace” might as well be the best name we could give to that breakthrough. “Grace” or better yet: call this no-thing-ness, this emptiness nothing at all.

Remember: “Shake it – it does not move; chase it – it does not go away. Bright and clear, you are always in it.” This the bowels of meditation.