Working many years in the legal field, I've seen the phrase, "time is of the essence," many times; I fully understand its meaning. What has always bothered me, though, is that the phrase doesn't seem to parse.
How can time be "of" anything? This phrase invokes time, itself, as a concept, in a way that "time of day" or "time of your life" does not.
And how can anything be "of the essence" of something else?