why do we pray?
We were talking about why people do or don't come to services, and more broadly, why we pray. That is, do we feel directly commanded to pray a certain liturgy three times a day, the way our traditional friends do? Do we feel that this is our only method of connecting with God? If yes (to either), where is everyone? (Mind, some of our traditional friends may ask the same question.) Why does the weeknight minyan so often consist of just my rabbi and me, and what would we be doing otherwise?
My rabbi believes, and I tend to agree, that people, by and large, come to our Friday-evening services for events, not for prayer. They come for a bar mitzvah, or a baby naming, or to hear a particular speaker. There is a dedicated core, people who come nearly every week as part of the community, but at any given service they are the minority.
Contrast this, I said, with our Saturday-morning service -- the real one, not the bar-mitzvah service. We have an established community; it's pretty much the same people every week, and we're there for the service and for each other, and not for external factors like on Friday night. I asserted that people who don't come for events come for community -- maybe also for prayer, but it's the community that dominates. (After all, you can pray at home.)
(Speaking for myself, I am there on Friday nights and weekdays for both prayer and community support. While I will seek out Shabbat services if I'm away from my own synagogue, I'm not diligent about weekdays. I mean, even in town, I don't go every day. If we were to declare our weekday evening service a failure and shut it down, I wouldn't start going elsewhere. But because we have one, I support it. Our Shabbat morning service, on the other hand, is something that really means a lot to me, and if something were to threaten its existence I'd be in for the fight.)
My rabbi believes that people -- by which I think he mainly means modern Reform Jews -- are looking for three things in a prayer experience: intimacy, intensity, and authenticity. Our Shabbat morning service certainly has all three characteristics, but I think that can only happen in a strong community. I don't think you'd get that at the bar-mitzvah service. While our service does get visitors who seem to fit right in to the community (it appears to me -- some may be reading this and I invite you to speak up), it's because there is a strong foundation of an established community. Friday night also has an established community, but it's not large enough to provide intimacy and intensity for everyone.
We ended up talking a little about the question I raised here a while back of how do rabbis pray?. He pointed out the irony -- that those who are most motivated end up being the least able to actually pray in a community. This is another reason our Shabbat morning service is so valuable -- while yes, the rabbi is in charge, the service can practically run itself, and he's much freer to be "just a congregant" there.

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It's speaking here of your own prayer, not prayer on behalf of the congregation, right? For example, in the chazan's repetition of the Amidah you would expect to find the fixed text. A lot of Reform services (and a fair number of Conservative, in my limited experience) involve the congregation reading together, or the service leader reading on behalf of the congregation. Personal kavanah, of necessity, takes a back seat when that happens (which is why the service must also provide "personal" time).
I don't believe that we are irretrievably wedded to a particular text in personal prayer; in fact, I've argued against that viewpoint. However, at the congregational level there is an expectation that you won't stray too far from the norm. Also, you said "put in additions in places where there is room for it" -- that "where there is room for it" is sometimes violated in favor of just doing it willy-nilly. For example, using Mishkan T'filah you could end up with the congregation together reciting a piece of alternate poetry where you expected "Avot" to be. I'd be bothered by that.
When it's just you and God, though, I think it is important to meditate on the meanings, and if an alternate text helps you do that, go for it.
correspondence of the parts of the amidah to the Seven Shepherds:
Thanks for sharing this! That's interesting, and I need to think more about it.
2) There are places for "creative" services as well.
This is a good point. I hadn't been thinking of things like unveilings, britim (boy does that word look funny), weddings, and so on. A characteristic that these have in common, and that regular weekday or shabbat or holiday davening lacks, is that it's focused on a particular family. When the service is oriented toward a specific group I would expect customization to make it more suitable to that group, like what you did.