Whenever an extra-biblical doctrine is created and taught broadly this question must be addressed: “What is the possible harm?”
As is pointed out in FAQ 17 there may not be any harm at all depending on what the Christian believes the new doctrine teaches, or, in how the Christian acts upon what he hears. On the other hand, there are also many possible unhappy outcomes when embracing an extra-biblical doctrine. First and foremost is the temptation to make the new extra-biblical doctrine obligatory and bidning on all. This is called legalism. It is most easily identified by seeing things stated as if they were commandments from the Word that must be obeyed, yet, oddly, these commandments are not actually found in the Word.
