Very esoteric at first glance, with lots of adjunct Buddhist terms (kayas! shunyata!) to learn in order to parse its meaning. But it is so incredibly liberating (unsurpassable!). I’ve spent some time with this one recently and feel like I’ve finally cracked the shell and started to access its incredible potential power to change our lives.
The four kayas are basically the stages the mind goes through when it encounters something new: uncertainty, followed by a hazy, unorganized idea, which begins to gain energy and coalesce into some kind of shape, and then finally clicks into place in the present moment. As Achayrya Judy Lief points out, there is not a lot of difference between confusion and the process of awakening. Confusion is like the first two stages, but as you observe this process of your mind, you know the next stages will follow as you awaken to a new understanding. Thus confusion is basically empty, because it is a transient mental state that represents the first phases of awakening. The mind that recognizes its own confusion as a passing and empty experience (shunyata) is the least attached, and therefore the most protected of all.