In modern terms St John of the Cross was talking about the ego.
The ego creates the false images of self, which we want the world to notice.
It dwells on the past, regretting mistakes that were made that didn’t serve the ego, or the one’s that boasted the ego into greater false self images.
It also dwells on the future, planning out how to make the false self-image greater in the eyes of others.
The weakest place for the ego is the present moment, which is why St John says to detach from these other things.
God dwells in the present, because it’s the only reality that exists.
Jim