Why should we obey is the question. Because it’s good for us seems to be a rather question begging answer. Nor does it seem to be an essential explanation in that there many things which we do which are good for us, which are not strictly obedience so how does the explanation differentiate obedience from any other generic good?
So the question still stands. The only real reason for obedience is if we think that the people above us are better. I think we can gleam that from certain phrases in the summa
"Obedience proceeds from reverence, which pays worship and honor to a superior, newadvent.org/summa/3104.htm#article5
So obedience is given just in the case that honor exists in the superior. But honor is always given for some objective superiority or “betterness” that someone else has. Therefore it seems that obedience exists just in the case that someone better than you asks you to do something from an authority derived from his merits.
So when we ask about papal authority, or any kind of authoritativeness, I think we should
ask what honor that person has, by ways of justifying our obedience.
As for the Iraq question, I was just saying that if it is possible for all the clergy to teach that the Iraq war is evil, then it would be possible for an opinion to be authoritative but this is wrong and so it is not true that anything said by the clergy is authoritative. For I think that you said that (paraphrase) “what a bishop says goes as far as how to practice Catholicism”. Obviously, to not support the Iraq war is a way to practice Catholicism so I think it would fall under the bishop’s authority.
So somehow I suppose you don’t think that the Iraq question can be made into a teaching?
I’m sure that honor comes from God and the sacrament of holy orders, but does this extend to anything a bishop says about how to practice Catholicism? Am I misinterpreting what you said about the power of a bishop?