Read Matthew 13:44-58.
"Therefore every scribe who has been trained for the kingdom of heaven is like the master of a household who brings out of his treasure what is new and what is old." (Matthew 13:52)
Walter Brueggemann (and I'm sure others) have compared the preaching task in our time, a time of great change, to that of a scribe - and particularly to this kind of scribe "trained for the kingdom of heaven." I find it a helpful descriptive metaphor - not just for preachers but for ministry in this time and place.
On the one hand, so-called conservatives feel that we are in danger of losing that "old time religion" - the "faith of our (mothers and) fathers" that they sometimes forget needs to be "living still." On the other hand, so-called progressives sometimes act as if this is the first time in the history of God's people that we have faced change. Instead of drawing on the helpful and sometimes neglected parts of the "tradition," they sound sometimes as if the baby is being thrown out with the bathwater.
Now I know that I've set this up in a very Anglican way. No one wants to be labeled this kind of so-called conservative or so-called progressive! We all know that the real challenge is to figure out what traditions are worth carrying on and what needs to die - and it is precisely as we become specific that we begin to disagree. But it is, I think, the right way to frame the question (or questions) - out of which may emerge a whole variety of answers and experiments that we live with for a while.
Apparently the height of Constantinian Christianity in the USA was in post-war America, from the 1950's to the 1970's. Especially in growing suburbs "everyone" went to church and the Sunday Schools were full. But as Kierkegaard once asked of "Christian Sweden" - how to be a Christian in Christendom? We speak of the decline of church attendance but it's because we start in 1950! In fact, if one takes the longer view and looks at the Church in the eighteenth and nineteenth centuries there is a different story. And yet so-called conservatives and so-called progressives get fixated on asking the same questions based on the same data and the same old debates.
The work we have been given to do, I think, is about discerning what from the past will serve God's reign, and what does not. It's about wine and wineskins. We can't just quote Jesus out of context to fit our agendas; we have to follow him and take our lead from him. Being the Church requires more than learning which notes to play - it requires a willingness to improvise - under the Spirit's guidance.