As we have learned (see above, daf 46), Grace after Meals consists of four blessings, the first three of which are of Biblical origin, based on the passage in Sefer (8:10), while the fourth blessing is either derived from that same verse, or else it is a later, Rabbinic, addition. The baraita that is the source for this teaching appears on today’s daf.
At the same time, today’s daf also contains the following teaching, in which Rav Naḥman credits the origins of the four blessings of Grace after Meals to various Biblical characters, including those who lived after the Torah was given.
Moses instituted for Israel the first blessing of: Who feeds all, when the manna descended for them and they needed to thank God.
Joshua instituted the blessing of the land when they entered.
David and Solomon instituted the third blessing: Who builds Jerusalem, in the following manner: David instituted “…on Israel Your people and on Jerusalem Your city…” as he conquered the city, and Solomon instituted “…on the great and Holy Temple…” as he was the one who built the Temple.
They instituted the blessing: Who is good and does good, at Yavne in reference to the slain Jews of the city of Beitar at the culmination of the bar Kokheva rebellion. They were ultimately brought to burial after a period during which Hadrian refused to permit their burial.
The Rashba points out that if the first three blessings are obligatory by Torah law, how is it that they were not recited until the days of David and Solomon? He explains that the basis and fundamental essence of the blessings are alluded to in the Torah, but the formulae of the blessings were instituted over time by those Jewish luminaries, and changed according to the needs of the times. It is clear, for example, that the blessing that we say “Build up Jerusalem, the holy city, speedily in our time” is a changed blessing that could not possibly have been recited in King Solomon’s time.