Moshe praises Hashem as “HaKeil haGadol vehaGibbor vehaNorah”. That is the praise Anshei Kenesses haGedolah codified into Birkhas Avos, and thus that list somehow pasts muster. R Chanina (Megillah 25a) scolds a Chazan for ad-libbing beyond those three adjectives.

But we do have many more praises in Birkhas Avos! How is that legitimate?

The Vilna Gaon says that this four-description pattern, the noun and three adjectives, is actually all we do say in this berakhah is elaborations on this four-fold theme.

There is something of a conflict between Tuvekha – Your Good, and Yeshu’asekha – Your salvation. If everything were going well, we wouldn’t need saving.

We see the same dichotomy repeatedly in Birkhas Avos…

A lot is hiding in the word “וּמֵבִיא – and brings”. Hashem won’t send the Melekh haMoshiach. He will come with (so to speak), bringing the person who will help us bring His Plan to culmination.

The Jewish People established a relationship with Hashem, even before Sinai, with avos who acted with chessed….

Rabbi Y.B. Soloveitchik takes the possessive in “Elokei Avraham, Elokei Yitzchaq, vEilokei Yaaqov — the G-d of Avraham, the G-d of Yitzchaq, and the G-d of Yaaqov” in a sort of mystical way: that one can somehow take possession of the Creator.

I want to say something similar, but with a more rationalist presentation:

The posessive could be used to show that two things exist in relation to each-other in a number of different ways.