This post, by Boruch Clinton, originally appeared on the B'chol D'rachecha site.
If we (theoretically) removed all innovations to the modern siddur which were added in the past 500 years, we’d probably spend considerably less time in shul. And from a halachic perspective, that’s a problem. So let’s talk about the prohibition of delaying a congregation (טרחא דציבורא).
We’ll begin with the Gemara (Berachos 12b):
בקשו לקבוע פרשת בלק בקריאת שמע ומפני מה לא קבעוה מפני טורח ציבור
The rabbis sought to include Parashas Balak in the recital of the Shema. Why did they not include it? Because it would delay congregations
It seems there was a compelling reason to add (at least) one more paragraph to the Shema, but it was ruled inappropriate solely due to the fact that countless Jews through countless centuries would be forced to spend more time davening. (Although we see from the subsequent Gemara that, had it been possible to add just the words “כרע שכב כארי וכלביא מי יקימנו" the minimal time delay would not have been a problem.)
