I have been looking into this and while I believe that God's teachings are far more important than God's miracles. None the less God's miracles are important. So how do you differentiate Cohba or magic from God's power in order to prevent such things from undermining God's miracles.

The easiest way is to create a number of rules. For example.

You can not bring back the dead. This ability is reserved for God Alone.
Ect.

What do you think?

I would express the system of magic as a logical science pertaining to it's use in the story-world. Not only would this allow for deeper immersion into the environment your weaving but allow the reader to understand that there are things going on behind the story. New advances in the fields of magic and such. You need not even go so far as to call it a science. simply let it be an ever present but hidden thing that is as naturally a part of the environment as say rocks or trees.

Miracles have the ability to laugh in the face of logic, reason and cause. For God needs none of these.

My two cents anyway.

I agree with Whackem. Magic/cobha in books shouldn't be "random" or "just there," but regulated by a strict set of rules so then miracles are differentiated from magic/cobha because it doesn't follow the rules of magic in that world...

Another solution is that if there don't appear to be strict rules of magic/cobha, God's miracles can be differentiated by how much more powerful they are than the other magic so that they are clearly in a different realm. I'm thinking here of the showdown between Moses and the Egyptian magicians, where God's miracles trumped the magicians all the time until they finally gave up and saw that this was above what magic could do...

I hadn't thought about this before, though, and am interested to see what other people's takes on this are.

Ah but it is implied that the Magicians of Egypt where nothing more than Fakes. Ill get back with you for the scripture.

Given what cobha is, isn't the question rather unnecessary? Isn't physics our world's cobha? And yet no one asks "how do you differentiate physics from God's power in order to prevent such things from undermining God's miracles?"

Think about it this way. If Person A can turn water into wine. Normally that would make him special. Unless of course person B through Z also had that ability. That ability would be common and unimpressive. There are primarily two ways to overcome this. Person A is just so ridiculously powerful he could turn the ocean into wine or Person B through Z cannot turn water into wine. For instance I have a number of things people cannot do with Aether in my more secular work Aetheria.

You can not change exiting matter from one state too another. (Water into wine, Lead into Gold, Ect.)
You cannot bring back the dead. (Resurrection)
You can to create something from nothing only. (God creating the world, The feeding of the 5000 Ect.)

Is it? I mean, I'm not overly disbelieving of that theory, but I do think that there is some power in the satanic art of magic when God allows it...

I still don't get it. Are you trying to set up your cobha so that the miracles God does/did in this world will still seem miraculous there? If so, I don't see that that's necessary. Our world has its own cobha that makes those signs/miracles impressive. In another world where everyone could do that stuff, God would presumably use different signs.