Eckhart wrote:It means to inhabit your body fully. to always have some of your attention in the inner energy field of your body. To feel the body from within, so to speak. Body awareness keeps you present. It anchors you in the Now.
"Inhabit body" is very similar to "be alert". Whenever I flip on the "high alert" switch, I am inhabiting my body. I feel my body from head to toe.
There seem to be some subtle differences between them.
1. Inhabit the body is only one effect of be alert.
When I flip on the "be alert" switch, it is like saying: ok, I am going to sense the whole universe with every cell of my body. There is a strong total body sensation. But additionally, I am quite aware of the universe outside my body.
2. When I am on "be alert" mode, the emphasis is on the external world. Although, there is very strong inner sensation (maybe inner organ movement, total body blood flow increase a lot due to mind shuting down). Ironically, the stronger my desire to sense the outside, the stronger the inner body sensation.
In that sense, don't try to sense the inner body. Just sense the external world. You end up sense the whole world (inside and out)
3. "Inhabit body" can be done while doing meditation in a quiet place at home (close eye). "Be alert" can be done at many more situations and can be combined with many activities. In my opinion, Eckhart does "be alert" while giving a talk. (he calls this "teach from presence").
If you want to put attention inside your body at a noisy place with eyes open, this creates inner conflict. As the visual and audio signal wants to take your attention to the outside. But if you do the "be alert" and use your total body to "feel" the whole world, everything is aligned perfectly. Totally effort free, fully present. One can do it as often and for as long as he desires without feeling tired (and greatly boost his health and realtionship with other people).
Just as a side note, even when I do meditation inside my quite home (eye closed), I often use the "be alert", use my body to sense the outside. Not paying attention to inside. This often leads to deeper peace, and more dramatical inner body sensation.
4. if you see the universe as the extended body. Then "inhabit body" and "Be alert" may be fully synonymous.