When you have eaten your fill, you shall bless YHVH your God for the good
land that He has given you. (Devarim 8:10)
These words are the explicit source for the commandment of Birkat haMazon
- blessing God after eating a meal. There are several blessings in the
HaZan - praise for God, who sustains the world;
Birkat Ha'Aretz - thanks to God for everything, focusing on the
Boneh Yerushalayim - petition to protect and rebuild Jerusalem;
HaTov vehaMeitiv - general praise and thanks for God.
In addition, when three or more men eat together, the Birkat haMazon is
prefaced by the invitation known as Zimun. The Gemara (Berakhot 48b)
When you have eaten your fill, you shall bless - Birkat haZimun;
the LORD your God - Birkat haZan;
for the...land - Birkat haAretz;
...the good (land)... - Boneh Yerushalayim;
that He has given you - HaTov vehaMeitiv.
From this piece, it seems clear that all five of these blessings are sourced in the Torah. Although differing opinions are presented regarding HaTov vehaMeitiv and Zimun, the basic formula of the
blessings is, according to all opinions, mandated by the Torah - D'Orayta.
THE HISTORIC ASSOCATION
Earlier on that same page in the Gemara, we are told that Moshe composed
the Birkat haZan when the Manna fell, Joshua composed Birkat ha'Aretz
when the people entered the Land of Israel, David and Solomon composed
Boneh Yerushalayim at different stages of the building of the city, and
the Rabbis at Yavneh composed HaTov vehaMeitiv in response to the burial
of the martyrs of Beitar.
These two statements are apparently in conflict: From the first, it seems
that at least three of the blessings are mandated by the Torah; from the
second, it seems that these blessings were created at different point in
history; such that at most, the first one was "in operation" at the time of
the Torah, and the rest must be Rabbinic obligations.
One possible approach depends upon an understanding of form and text within
the context of prayer. According to many Rishonim (see Rambam, Ch. 1 of
Hilkhot Tefilla, Ramban's comments on Sefer haMitzvot, Shoresh 1 etc.),
there are several Mitzvot in the Torah which are presented in a most
general way - and later generations (prophets, sages, custom) create form
and, eventually, specific texts through which these Mitzvot are fulfilled.
For instance, according to several Rishonim (Rabbenu Yonah, Tosafot,
Raavan), the Mitzvah of reading the Shema is essentially a Mitzvah of
reading words of Torah - and the rabbis decided upon this particular text.
According to Rambam, daily prayer - as mandated by the Torah - has only the
most general form - praise, request and thanks. It was later rabbis (Ezra
and his court) who formulated the specific blessings. (Other examples
include Kiddush, Hallel (according to Ramban), teaching the Exodus to our
children on Pesach night, confession on Yom Kippur etc.)
We can posit the same here. The Torah commands us to bless God after
eating by praising, thanking and beseeching Him. The Torah itself not only
provides no text for this blessing, it also provides no area of content.
When the Manna fell, Moshe composed HaZan, praising God for His
in sustaining the world. He not only composed this blessing, he also
ordained that it be recited after every meal.
When the Torah was given, that blessing, along with the general blessings
of (atopical and contentless) thanks and request, were the proper way to
fulfill the command of Birkat haMazon.
When Joshua led the people into the Land of Israel, he "fixed" the
"thanking" component to revolve around the Land. Clearly, the content of
his blessing was different than ours, insofar as his likely included
mention of the unfought battles for the Land. The third blessing was still
a generic request.
When David build Jerusalem - and when Solomon constructed the Temple - they
each "pinned down" a component of request (at that time it involved
"protecting the city" - not "rebuilding it" as we request).
In summary, there were three stages in the development of Birkat haMazon:
The Torah's command, to praise, thank and beseech God after eating;
The historical targeting of specific content areas for each blessing;
(Moshe - praise for God's sustenance; Joshua - thanks for
David/Solomon - request for protection of Jerusalem and the Temple)
The evolution of a (more or less) fixed text, after the destruction of
As we praise, thank and beseech God after a meal, we also understand that
by doing so we not only strengthen our connection with the Holy One, who is
Blessed - but also with our history and our Land.