The Bais Halevi says that prior to the breaking of the first set of Luchos, there was to be no difference between Torah Sh’bichtav and Torah Sh’beal Peh. Torah Sh’beal Peh was supposed to be a written portion of Torah Sh’bichtav. The breaking of the Luchos was the event that changed the character of Torah Sh’beal Peh from a written format to one that was to be handed down via the Mesorah. When Moshe delivered the Brachos U’klalos in Parshas Ki Tavo, this difference in format between Torah Sh’beal Peh and Torah Sh’bichtav had already been established. It is interesting to note that in the covenant in Parshas Mishpatim that revolves around the Brachos U’klalos that are mentioned in Parshas Bechukosai, the Torah uses the phrase “Al kal hadevarim” while in Devarim, it uses the phrase “AlpPi hadevarim“. The difference is that in Parshas Mishpatim, Torah Sh’bichtav and Torah Sh’beal Peh were to be transmitted in the same way, hence the use of the word kol, all. In Parshas Ki Tavo, where Torah Sh’beal Peh had already been established as an oral tradition, the Torah uses the phrase “Al pi” to indicate that Torah Sh’beal Peh, as a unique entity, was included in this covenant. After the breaking of the Luchos, Torah Sh’bichtav alone was to be written, while Torah Sh’beal Peh was given to Moshe and he was charged with the responsibility of transmitting it to Bnei Yisrael, hence the term Mesorah.
We can now explain the role of Moshe in each set of Brachos U’klalos. In Parshas Bechukosai, where everything was to be included as part of Torah Sh’bichtav, Moshe’s role was limited to that of a simple messenger, he was not yet considered to be Rabban shel Yisrael, teacher of Israel. Hashem alone is the mashbia, the One who administers the oath, to Bnei Yisrael. Hence the Gemara says that Moshe said these Brachos U’klalos mipi Hagevurah. However, with the second Luchos, Torah Sh’beal Peh was given exclusively to Moshe, Toras Moshe. He became Rabban shel Yisrael, teaching it to each and every member of Bnei Yisrael and was rewarded with the rays of light that shone from his face. Therefore the Gemara says that Moshe said the second set of Brachos U’klalos mipi atzmo, to indicate that he was the mashbia of Bnei Yisrael and the second covenant, that he was a party to, obliged Bnei Yisrael to follow Torah Sh’bichtav and Torah Sh’beal Peh.
The Rambam asks (on the verse Lo kam navi od byisrael k’Moshe) that in Parshas VaEira, Hashem told Moshe that He appeared to Avraham by a different name. The Midrash comments that Hashem said that the patriarchs were on a higher level than Moshe. The Rambam explains that Moshe must be looked at from two perspectives: before and after the breaking of the Luchos. Indeed, prior to the breaking of the first Luchos, the patriarchs were on a higher level than Moshe. Though Moshe was the messenger charged with the task of relating the first set of Brachos U’klalos and serving as the intermediary for the first covenant between Hashem and the people, this did not, in and of itself, raise him above the patriarchs. Only with the second Luchos, did Moshe become the adon haneviim, the greatest of all prophets. Essentially, Moshe became a part of Torah. This greatness was expressed through Moshe’s role as teacher of Israel, transmitter of Torah Sh’beal Peh and the mashbia Bnei Yisrael obligating them to keep for all time the Torah Sh’beal Peh that he taught them. The covenant entered into in Parshas Ki Tavo was different in that it included both Torah Sh’bichtav and Toras Moshe, Torah Sh’beal Peh.