Signing off the bracha of 'magen Avraham' with just Avraham

Question

In Parshas Lech Lecha 12:2, the pasuk famously reads:

וְאֶֽעֶשְׂךָ֙ לְג֣וֹי גָּד֔וֹל וַאֲבָ֣רֶכְךָ֔ וַאֲגַדְּלָ֖ה שְׁמֶ֑ךָ וֶהְיֵ֖ה בְּרָכָֽה׃

I will make of you a great nation, And I will bless you; I will make your name great, And you shall be a blessing.

Rashi there writes:

והיה ברכה. הַבְּרָכוֹת נְתוּנוֹת בְּיָדְךָ; עַד עַכְשָׁו הָיוּ בְיָדִי, בֵּרַכְתִּי לְאָדָם וְנֹחַ, וּמֵעַכְשָׁו אַתָּה תְבָרֵךְ אֶת אֲשֶׁר תַּחְפֹּץ (בראשית רבה). דָּבָר אַחֵר ואעשך לגוי גדול זֶה שֶׁאוֹמְרִים אֱלֹהֵי אַבְרָהָם, ואברכך זֶה שֶׁאוֹמְרִים אֱלֹהֵי יִצְחָק, ואגדלה שמך זֶה שֶׁאוֹמְרִים אֱלֹהֵי יַעֲקֹב. יָכוֹל יִהְיוּ חוֹתְמִין בְּכֻלָּן, תַּלְמוּד לוֹמַר וֶהְיֵה בְּרָכָה, בְּךָ חוֹתְמִין וְלֹא בָהֶם

והיה ברכה AND BE THOU A BLESSING — Blessings are entrusted to you; hitherto they were in My power — I blessed Adam and Noah — but from now on you shall bless whomsoever you wish (Genesis Rabbah 39:11) Another explanation is: AND I WILL MAKE THEE A GREAT NATION, this alludes to the fact that we say in our prayer “God of Abraham”; AND I WILL BLESS THEE — that we say, “God of Isaac”; AND I WILL MAKE THY NAME GREAT — that we say, “God of Jacob”. One might think that we should conclude the benediction in which these invocations are recited by mentioning again the names of all the patriarchs — the text therefore states “Be thou a blessing” meaning, with you (i.e. with your name only) shall they conclude the benediction and not with them (their names) (Pesachim 117b). (Sefaria translation)

So we see based off the Gemara in Pesachim that rather than conclude the bracha with all the avos, we only do so with Avraham.

The Maharal in Gur Aryeh helps provide a reason why:

בך חותמין כו'. ואם תאמר מאחר שכלם אבות למה לא יחתום בכולם, ואין זה קשיא, דאין חותמין בשתים, כדאמרינן במסכת ברכות (מט.). ואם תאמר מאי שנא אברהם, נראה מפני שהבן בכח האב ואין האב בכח הבן, ולכך בחתימת אברהם יש חתימה יצחק ויעקב. ואלו דברים הם אמת למבינים, והוא דבר נעלם

With you (i.e. Just Avraham's name) they conclude the Bracha etc. And if you will say since they are all fathers why not sign off with them all (i.e. say Avraham, Yitzchak and Yaakov)? And this is not a problem, since we do not conclude with two (themes). Like we say in Brachos 49a and if you say how is Avraham different it would seem that the son is in the power of the father and the father is not in the power of the son , and therefore included in the signing off of Avraham is both Yitzchak and Yaakov. And these words are true to those who understand them and it is a hidden matter.

So my questions are as follows:

1. How are the individual Avos to be regarded as a separate themes? Surely, whilst they embodied different core middos e.g. Avraham - chesed, Yitzchak - gevurah and Yaakov - emes/Torah they all still represent the concept of being our forebears, i.e. the Patriarchs who established the standard for us all?

2. And if we say like the Maharal that the 'son is in the power of the father' and thus Avraham encompasses all of them - why then do we make a point of starting the bracha mentioning all three. Surely there too we could just say Avraham?

Answer 1

In regard to your second question, the answer is that all the Avos are separate, and deserve to be mentioned separately. However, it is not possible to mention them all in the closing, so we mention the one that includes the most, which is Avraham.

Answer 2

From the perspective of the binyan (structure) of Chesed, Gevurah and Emes, Chesed is a "child element", not an av. I.e. chesed is not intrinsically associated with the koach ha'holadah (power to father/beget). This is because chesed implies there is happiness/fulfilment in the current state so there is no need to be molid (beget future generations). Therefore the koach ha'avhus of Avraham Avinu (that which he was a "Father" to the Jewish people) is not a toldah (derivative) of his middas ha'chesed.

From this perspective, Yitzchak and Yaakov were not toldos (derivatives) of Avraham's middas ha'chesed. Rather each created anew their own derech (way) in serving Hashem. That is why each is mentioned separately in the berachah. However, from the perspective of koach gufa, i.e. from the perspective that is was Avraham who had the perspicacity, endurance and strength to found the Jewish people, Yitzchak and Yaakov are included in Avraham, because that is where they got their own perspicacity from.

Therefore we can conceive of the entity of the Jewish people in two ways. We can consider the Jewish people to be a coalescing of the individual avodah of each of the avos or we can consider the Jewish people to come entirely from the koach of Avraham.

Relative to the second perspective, we are mesayem (complete the first blessing of Shemone Esrei) with just Avraham, as he is the amud ha'kol (foundation of everything). Relative to the first perspective, we mention each av separately within the berachah.