At the back of one of my siddurim, I found something called סדר מעמדות and it seems to have a part of the Torah and Mishnah, etc, that is divided from Yom Rishon (=Sunday) to Shabbos. What is the purpose of it, and its history?
Originally, there was less text, and it was said by the anshe maamad, the non-kohanim non-l'viyim who were on duty as representatives of all Jews in the bes hamikdash. By the time of the g'onim some people were saying it daily in commemoration (much as we say korbanos daily); more texts got added later. I don't think there was ever a time all religious Jews said it. (My source.)