Awesome, that makes a lot of sense, I think.

So would it be correc to say that being means the extent to which a thing's essence is currently existing/actual? Which, as you said, is why God's has the most being (as pure act his essence of existence is always fully expressed) and why we, as material beings with a great deal of potential left unactualized, have less being than angels? 

Thanks so much for the quick response, that's really helpful.

I'm reading through Feser's Aquinas and I'm really stuck on what 'being' is supposed to mean; I've had to stop reading altogether as I've gotten to the Five Ways because I can't understand them without this more fundamental concept.

What I've gathered so far: 'Being' can't mean the same thing as 'existence' since almost everything can have being without having existence (except God). It also apparently has a hierarchy, as God has more being than any other (though he has it in a difference sense than we do). But does that mean 'being' something is like an essence or a description of a thing? I'm uncertain.

I've greatly appreciated the book so far, but I'm reading it on my own and am feeling about portions of it as the Etheopian eunich. If if someone could give me a clear, concise definition of 'being' as Aquinas/Feser use the term, I'd be really grateful.