When Meister Eckhart deliniates the "ground" and "powers" of the soul, what is he differentiating? I'd like to know where to look for scholarly articles that could help elucidate unclear points in ancient writings. For instance, Desert Fathers speak a lot about "heart", "spirit", "mind", "thoughts", etc., and consider all to be different. 

Specifically, I fail at mapping those notions to something more understandable in modern terms. Meister Eckhart, in particular, clearly separates "ground" of the soul ("spark", "castle") from "powers" of the soul (higher intellect, will, lower intellect, emotions, etc.). I don't clearly understand the difference. 

Moreover, I sometimes fear that the difference cannot be grasped in verbal terms, because analytical thinking might be constricted to "powers" of the soul in Eckhart's terms. That said, any direction in helping to describe these otherwise ineffable concepts would be useful.
One thing I like to point out in discussions like this one is that we are often talking in English about words and ideas from languages that we do not speak. For example where the word SPIRIT is used in the new testament passages and in the writings of many early Writers after that time it is the Greek word Pneumos which literally means air but also breath, vital essence, mind-set and a few other things dependant on context. So for example the Holy Spirit is literally renderable as The Fearsome Breath of God. When they spoke of evil spirits this was sometimes a reference to the bad smell on the breath of a sick person (literally bad breath). 

My point here is that it is helpful to understand the word usage from the original language and where these ideas have come from as we hold them today. Some ideas like Spirit and Thoughts might well have been seen as synonyms or something close to that back when they were first penned and definitely the word choice in many cases would have been to underscore a particular aspect of what the writer was saying. 

It might be easier to try and understand these ideas in terms of the gist of what the writer was trying to convey first and then drill down to the specifics later. Of course that is only my own approach.