Creeds

So then; how and why are the Creeds authoritative or to put it differently in what sense are they? The question should be qualified a bit. What Creeds are we talking about?
Two: the Apostle’s and the Nicene; for we are talking about the ecumenical Creeds; statements of faith which express the bare bones of the Christian tradition.
It has been noted that most every heretic that has arisen to plague the Church has an “air tight” doctrine of scripture. For example most, if not all, of those espousing Arianism would be in near or complete agreement with the WCF on its doctrine of Scripture; that is no Arian worth his or her salt would argue against Divine authorship of both the Old and the New Testament scriptures; which is great; as far as it goes, but the roots of heresy are not found here though the error is. Recall then an earlier definition of heresy; defined as a private opinion. Some early churchman described it thusly; by analogy heresy can be pictured as, on the one hand, a group of men sitting together on a couch (the orthodox) opposed by an individual sitting all alone (the heretic).
The Creeds then, as consensus, lay out in a concise fashion what the church has understood the Scriptures to teach on specific subjects. And this is an important point for they are the teaching of all the church historically on what scripture says. Herein we find the authority; the Creeds are simply concise statements of Scripture’s statements, not arrived at by individuals, but by councils of men (presumably) appointed to the task by Christ Himself (see Ephesians 4).
But you may ask “is it possible for church councils to err”? Indeed they have and do but recall that the two Creeds in question are ancient and have stood the test of time and still form the consensus of men who, at other points, have been in complete or near complete disagreement on others. The point then is this: Protestant and Roman catholics have much to disagree upon but they are in agreement on the Creeds and that must carry some weight. It must be maintained The Holy Spirit in some sense still moves and directs the church. To deny this is to call into question the Protestant Reformation and to relegate it to the opinions of men.