GraceSeeker your thoughtful, intellectual responses are always so very much appreciated; thank you!
As to the last point. I did intend to suggest that in the early days of the church, theology, it seems, was even more broad and vague than today. The significance of the Apostles Creed might be different today with denominations with hundreds or thousands of years of established history, now.
I share your thoughts on the necessity. The virgin birth doesn't seem like an excluder, like you can't be Christian without affirming it. In my sermon when I covered that, I suggested that a belief in the virgin birth affirms the unusual and miraculous way in which Christ came into the world and, of course, brought up the passages in Isaiah that could be translated to say "Virgin" by some scholars. (Young woman is the direct translation but some scholars suggest that, in that context, it was a polite way of saying 'virgin'), but I also discussed the shaky history of the virgin birth belief and how I do think one can remain Christian without believing in the virgin birth. I, personally, don't have reason to believe it isn't true.
However, issues like the Resurrection do, to me, seem to cross a line. I have been so burned and hurt by being called, or having my friends called, non-Christian because of some sort of dissenting belief. Anything from human sexuality (and friends on BOTH sides have been called non-Christian by the other side on that one); to women in ministry (TODAY, in fact, I was told that any church that Ordains women is evil and corrupted by Satan and that I was complicit in the downfall of Christianity. SHEESH), even to beliefs about connectionalism (congregationlists who suggest any church that isn't democratically led by some group of lay-people is evil). So I really, really don't like saying "You cannot call yourself Christian if you don't believe X". But, as much as I hate that, failing to affirm the resurrection sure is close.
If I were to define Christian as simply as possible, I think it might be "One who believes that Jesus Christ is the source of salvation.", Not that salvation is what it's all about; BUT, that might be the most simple way I can think of to define Christian. But, inevitably, there are tangets off of that. Islam affirms the virgin birth of Jesus Christ in the Qu'Ran but doesn't affirm Christ's resurrection or his sovereignty as God. Clearly, there are some things that must make us "Christian", and I really think the resurrection has to be one of them. That Christ conquered death, just seems essential to me.
Sunday we're covering "and sitteth at the right hand of God the Father Almighty, from thence he shall come to judge the [living] and the dead." (Using the UMH traditional language, I've been changing it up by having us recite the creed; something we don't normally do, each week during these series, and changing it up by using different translations of the creed; including a Roman Catholic version which uses slightly different verbage, a more modern translation with updated language, included "Descended into hell" and "descended into death"; which became a component of one sermon to explain our belief that Christ did not spend time, literally, in hell. But a better understanding is that the Apostles intended for us to understand that Jesus was completely dead, not just in a coma. So he 'descended into death'). The resurrection will be the final week and the week after will begin advent. I haven't yet decided what I'm doing for advent. I may stick with the lectionary.
I, too, preach with themes for the year. This year mine has been "on purpose, with purpose". And I've had my congregation recite that with me throughout the year. Each sermon, my prayer is, that it will encourage us to do what we do as Christian on purpose (with intentionality, not just because it's what we've always done or what we're supposed to do) and with purpose. In preaching through the Apostles Creed, I'm trying to move us through muttering through it and not really knowing what it says; so affirming it and claiming it as a part of our Christian identity. So that, likewise, the Apostles Creed becomes something we do "on purpose" (not just because the liturgist says so) and "with purpose" (because it is who we are, as Christians).