Why do some Roman brethren of ours still think it heretical when, to my knowledge, it was never condemned as heresy by Rome? I am seeing this a lot in my interaction with other Catholics. Why is this such a common fault?

Also, can anyone recommend a good introductory word on the essence-energy distinction? I'd like to know more details about it and want to start from the beginning and work my way up (everything I've read and/or been told this far has come piece by piece.