7:
The fact that the text of the blessings of the liturgy was not originally fixed eventually led to three completely different outcomes. Firstly, there was no unaninimity between the various centres of Jewish learning. This is particularly true of major liturgical differences between Eretz-Israel and the other major centre Babylon (Iraq). While in the long run the Babylonian tradition won through and conquered the Jewish liturgical world, some vestiges of the ancient tradition of Eretz-Israel were preserved in the Ashkenazi liturgy. These differences were not only as regards the content of the b^erakhot, but sometimes even as to the exact wording of the concluding b^erakhah itself. For instance, the last b^erakhah of the Shema in our present liturgy ends Barukh attah Adonai ga'al Yisra'el [Who redeemed Israel (from Egypt)]; in the ancient liturgy of Eretz-Israel it ended Barukh ... Tzur Yisra'el ve-Go'alo [Israel's Rock and Redeemer].

8:
A second development was the fact that poets took the opportunity to embellish the liturgy with poetic compositions. Some of these were in place of what we would now call the "accepted" text, and some were lyric additions to it. Rav Sa'adya Ga'on [Egypt and Iraq, 10th century CE], for example, composed many "alternative" texts which became very popular. Unfortunately, most of these poets eventually developed a style that was extremely recondite - almost impossible to understand even in translation without copious footnotes! Yannai and Eli'ezer Kallir were among the early poets of Eretz-Israel (Yannai may even have lived as early as 6th century CE), and they had many successors.

9:
This literary flowering of the liturgy was eventually seen by many as a burden, and a movement began to exclude all embellishments and to restore a supposedly pristine text. This was first evident among a group of mystic pietists in Medieval Europe called "Ĥasiddei Ashkenaz". They wished to establish a text and preserve it by counting the number of words in each b^erakhah and giving them a mystic reason. I think we may safely say that two developments caused the gradual uniformity of text that we have today. The later kabbalists of the Lurianic school (16th century CE) adopted the stance of "Ĥassidei Ashkenaz that the text was to be seen as inviolate. Since many differing texts were available, they required each person to remain faithful to the liturgical text inherited by the family. This did not stop the Ĥasidic Movement in 18th century Eastern Europe from jettisoning wholesale its inherited Ashkenazi liturgical tradition in favour of the Lurianic liturgy (named for Isaac Luria, Eretz-Israel 16th century CE) which was firmly Oriental in its content. The other development that encouraged uniformity was, of course, the invention of the printing press.

10:
The last sentence of the mishnah is intended to prevent a unilateral truncation of the b^erakhah by the worshipper.

In our last shiur I gave reasons why certain mitzvot do not require a b^erakhah. Michael Bohnen writes:

I thought there was no required b^erakhah for peru u'r^evu [Be Fruitful and Multiply] because the circumstances do not enable us to recite it with the proper kavanah. Regarding circumcision, I know that some do not recite shehecheyanu at a brit in recognition of the infant's discomfort.

On the same topic Josh Greenfield writes:

One consideration that might also be relevant is the worry about wasting a blessing; i.e., if a child is not conceived, then one would have taken God's name in vain.

I respond:

I do not think that Josh's suggestion can be followed through. From the halakhic point of view, while procreation is one purpose it is not the sole purpose. Therefore, even if the mitzvah of procreation does not come to fruition in any given instance, the mitzvah of onah [regular sex within the marriage bond] has been fulfilled.

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