In Merriam-Webster Learner's dictionary, the word "essence" means:
noun [singular] the basic nature of a thing.
For example, the essence of love is unselfishness.
The word "essential" means:
noun [count] sth. that is basic or necessary---usually plural
For example, the essentials for success is ...
From the means, they are different. But are they really different? "The essentials for success are...." and "The essence for success is...." are the same in my opinion. So are "essence" and "essential" sometimes interchangeable in meaning? If ignore the single or plural form.