No doubt those who are accustomed to think of “essence” as being connected only with extracts of one kind or another, as essence of turpentine, essence of roses, find themselves at a loss when encountering this expression.
But some eighty years ago, especially in the phrase “of the essence”, it was a legal term, and its meaning was virtually that of “essential.”
Hence, when you sign a contract containing the term, “time is of the essence,” it would be well to understand that time is of the utmost importance in the fulfillment of that contract.