It means that energy has a few more properties that are not found in contingent things.
Energy
obviously isn't the necessary entity because it isn't an entity at all, it's a property. However, what are the properties required for something necessary?
So you can ignore it for the fourth time (at least) if I suggested the space-time manifold is necessary, would that make it "God" - what extra properties would it need?
Thinking of which there are things which disqualify energy from being the necessary entity.
Wow! Vlad's said something sensible!
For information though, there are theologies which have energy as a necessary entity.
They are wrong (at least with respect the the scientific definition of energy).