Full Idea
An essence is true in virtue of what the thing is in itself, but a necessary truth may be relational, as the consequence of the relation between two things and their essence. The necessary relation may be two-way, but the essential relation one-way.
Gist of Idea
Necessary truths can be two-way relational, where essential truths are one-way or intrinsic
Source
Vassilis Politis (Aristotle and the Metaphysics [2004], 2.3)
Book Reference
Politis,Vasilis: 'Aristotle and the Metaphysics' [Routledge 2004], p.46
A Reaction
He is writing about Aristotle, but has in mind Kit Fine 1994 (qv). Politis cites Plato's answer to the Euthyphro Question as a good example. The necessity comes from the intrinsic nature of goodness/piety, not from the desire of the gods.
Related Idea
Idea 13166 Essences are no use in mathematics, if all mathematical truths are necessary [Mancosu]