הלכה על ברכות 56:24

As a result of the emphasis on the collective and fixed aspects of prayer, the personal component, with its intense and fervent passion, is liable to be pushed aside. This is the meaning of R. Shimon’s warning: “Do not make your prayer fixed, but [make it] a plea for mercy and supplication before God”(Avot 2:13). Rabbi Eliezer similarly said: “If one renders his prayer fixed, his prayer is not supplication” (Berakhot 28b).

From the laws of the commandment is that which they, may their memory be blessed, said (Berakhot 31a) that a man is obligated to pray three times: during the day in the morning and in the afternoon; and one time at night. And these three prayer services were fixed corresponding to the sacrifices, as they would sacrifice the daily sacrifice of the morning and the daily sacrifice of the afternoon in the Temple every day. And they also fixed [prayer] at the beginning of the evening, corresponding to the limbs of the burnt-offering of the afternoon that would be consumed and continue through the whole night. And since this prayer of night corresponds to a matter from the sacrifices that is not an obligation - as, if the burnt-offering of the afternoon was consumed while it was still day, it would not be consumed at night - they, may their memory be blessed, also said (Berakhot 27b) that the night prayer service is optional - if a man has free time and finds the presence in himself to pray, he prays; and if not, he does not pray, and there is no guilt in that. And nonetheless, in every place today, Israel is accustomed to pray the evening prayer service consistently every night. And once they took it upon themselves in the way of an obligation, every one of Israel is obligated to pray it regardless. And likewise, they, may their memory be blessed, fixed a fourth payer on Shabbat days and holidays - and that is the one called the additional prayer service (mussaf). And it corresponds to the sacrifice that was added [on these occasions] in the Temple at the time that it was in existence. And they also fixed a fifth payer on Yom Kippur alone - due to the great holiness of the day and because of its being a day of forgiveness and atonement for all - and that is called the sealing (neilah). And the wording of all of the prayers was fixed by Ezra and his court. And on weekdays, they fixed that [we should] pray the eighteen blessings that are well-known in every corner of Israel, besides the blessing about the heretics that was composed by Shmuel the Little with the approval of Rabban Shimon ben Gamliel and his court, as it is found in Megillah 17b (and Berakhot 28b). And what are they? Three of them recount the praise of God, and three are thanks after it and twelve included the requests for the needs of all of Israel. And they, may their memory be blessed, arranged them according to the order that they are ordered today in the mouths of all of Israel: the first three are in praise of God, may He be blessed; the middle ones in request of their needs, and the last ones in thanks to God for all of the good that He does with us, Blessed be He. And afterwards their exact order was forgotten. But Shimon HaPakuli knew them and he arranged them according to the intended order, as Ezra and his court had ordered them: to first request intelligence, as if there is no intelligence, there is nothing; and afterwards, repentance, etc., as they are ordered. And on Shabbats and holidays, they only fixed that [we should] pray seven blessings alone, so as not to burden the community on the day of their joy: the first three, the last three and one blessing in the middle which mentions the matter of the day in it - each and every festival and Shabbat according to its content (Berakhot 21a). [This is the case] except for the holiday of Rosh Hashanah, which has nine blessings in its additional service: the three first blessings, the last three blessings and three others, which are malkhiot, zikhronot and shofarot. Everything is as the received tradition in the mouths of all of Israel, even in the mouths of the infants - there is no need to write at length about these matters. However you should know that in the additional prayer service of Rosh Hashanah there is a law that is a novelty from the other prayer services - that the prayer leader (cantor) can fulfill [the obligation of] the one with expertise [in the prayer, as well as] the one without expertise; whereas on other days, he cannot fulfill [the obligation] of the one with expertise. So will you find the matter if you merit to study in the true path.