Halden has a very productive discussion going on his blog titled “On Remaining Protestant.” Here is a paragraph from one of his comments:
“Apostolic succession is obviously the linchpin issue on which the ecumenical question turns (and within that of course is the question of the sacrament of orders). If apostolic succession is viable, then the onus is definitely on protestants and the ecumenical dice is loaded in favor of Rome. If apostolic succession is not part of the esse of the church, then the playing field is somewhat more leveled and perhaps there are modes of communion that could be established to bring about Christian unity that are more complex and diverse than simply a structural integration of protestants into the Roman Catholic church. “
I was driving my daughter home from school this afternoon, thinking about this discussion, and I came up with the following regarding Protestantism as a Sign and Promise:
If Protestantism is a sign, it is an indicator both of the Church’s poverty and riches at the same time. The Church is poor in that it does not possess the things it promises. It is forever giving away what it possesses. It cannot possibly contain the Holy Spirit in order to monopolize it. It cannot possibly prove by its history or experience that its wealth is rightfully owned. All that it has is a gift.
Protestantism is a promise that the Church, as she is, has yet to be realized. God’s message in us is that the Spirit of God moves where it wishes—now in judgment, now in blessing. The realization of this promise will come not by our effort, but as a gift.
ADKF 
Sometimes you just have to say ‘Amen’.
– Peace
Just to be clear, for me this was one of those times. Well said.
– Peace
Protestantism is also an effort to assert an earthly religious authority– “Scripture” — as an alternative to the Heirarchy of the Church.
But as people like Ellul & Stringfellow notice in actually reading Jewish & Christian scripture, the authority it ultimately asserts is the authority of God. So they stand up for God against the powers and principalities worshipped in conventional Christianity, and thereby say brilliant, wonderful, liberating things. But they don’t realize–They even deny–that God makes any of this available outside the specifically Christian traditions.
Quakers have an advantage in this. We (at first) stood for the authority of the Spirit first of all, finding the same messages in the Letter of scripture as almost an afterthought. We took “Christ enlightens every man who comes into the world” and applied it everytime & everywhere; hence arrived at a sort of Christian Universalism in which having heard of Jesus was not a requirement.
But it’s hard to keep a focus on the Spirit; many of us miss the point and drift into one idolatry or another, or seem to worship nothing at all–That’s the downside.
A teacher explained the relation between us thusly: Basing authority on what’s written tends to direct the attention into the past. So there’s a tendency for Protestants to forget (something Ellul & Stringfellow expressed quite well) that God is present and active also in the world outside the book. (That, she said, was the issue in which Quakers tended to resemble the Catholics. Historically, that is, because the presence of God is a downright alien thought to the Modern Mind [a common affliction these days, even if they like to call it ‘postmodern’!])