Here's how I might express the point of this passage ...
There is a practice to be pursued, Teachings such as the "Four Noble Truths" to pierce.
But piercing the "Four Noble Truths" is ultimately like searching for a mountain while on the mountain (the "Mountain of Emptiness" which cures the Suffering described in the Four Noble Truths).
One might run for years and years, lifetimes, ages ... around the mountain looking for mountain. That's one way to go about things.
Or, sit very still and find the mountain.
Or, walk while still .. or slowly run while still (that's more our Shikantaza way).
In any case, the mountain is there.
Also, is the mountain walking/running you ... or are you walking/running the mountain? Do you climb up the mountain, or does the mountain climb down your feet? So, are you and mountain and climbing separate?
In any case, have a good hike. :-)
Better than my mountain example as an image for "Emptiness", Hixon and Keizan convey it talking about "building a stairway in the sky" or "flying birds that fly fly fly but leave no traces."
Cook from 175
Hixon from 165