Yerushalayim, introduced at the end of Parshas Vayera as the location of akeidas Yitzchok, is Klal Yisroel's holiest site and the focal point of our connection to Hashem. Another introduction immediately follows at the beginning of Parshas Chayey Sarah, where we are told about Chevron and its acquisition by Avraham Avinu. The connection between the two cities run deeper than a superficial juxtaposition in the text of the Chumash. Chazal tell us that when Sarah Imeinu found out about the akeidah she passed away. It seems that as soon as Yerushalayim, the makom haMikdash, was established, Chevron and all that it represents had to be established as well.
The connection between these two cities is not only presented to us via their juxtaposition in the Chumash; it finds an almost eerie echo in the Mishnah as well. The Mishnah (Yoma 3:1) tells us that early Yom Kippur morning the sgan (supervisor Kohen) would ask if the time to begin the Divine service [i.e. Sunrise] had arrived, and would pose this question by asking, "Is the whole East light as far as Chevron?" The Gemara explains that Chevron was mentioned in order to, "evoke zechus Avos - the merit of our Patriarchs." Thus, Divine service starts with a mention of the Avos.
Our invoking zechus Avos is not merely an annual event. The truth is that every tefillah starts with zechus Avos saying, "The G-d of Avraham, the G-d of Yitzchok, and the G-d of Yaakov." And even when, in that same first beracha, we speak of Hashem's praises, we do so by referring to Him as, "the One Who remembers the deeds of the Avos, and brings the redeemer to their children's children." This beracha is deemed so important that the Shulchan Aruch (Orach Chaim 101) rules that it is the only beracha which must be repeated if one did not have kavanah when saying it, and even if one had proper kavanah in every other beracha one nonetheless must repeat Shemoneh Esrei! [The Rema disagrees but only for pragmatic reasons, not essentially.] It is surely nice to mention the Avos, and it is wonderful to incorporate their merits into our prayer, but why is it the most important part of tefillah?
The Rambam describes the appropriate kavanah of tefillah as being cognizant that, "one is standing before the Divine Presence" (Hilchos Tefillah, 4:16). Rav Chaim Soloveitchik demonstrates that it is this kavanah, rather than the meaning of the words per se, that is the critical kavanah for tefillah. While it is very important to think of the meaning of the words, failure to do so does not invalidate one's tefillah. Yet if one failed to focus on being in front of the Divine Presence, one's tefillah is invalid and must be redone.
This presents a much greater challenge than we anticipate, for Hashem has no physical form whatsoever, and it is almost idolatry to picture him as having one. How is a person to stand "before Hashem" when the very meaning of those words is so elusive? How does one "picture" that which has no image? Essentially, this is perhaps our greatest general challenge in tefillah.
The answer lies in one of the core elements of the parent-child relationship. A child explores the physical world through his own sense, but the conceptual world's basic building blocks are transmitted from parent to child. The concepts of good, justice, responsibility, etc. are spoken about by parents and absorbed by children. A parent may not provide a dictionary definition of the word "responsibility" when he uses the word, but as he says it the tone, body language, context, and so much more are absorbed by the child. The child may also never have a precise definition of the word, but he certainly has a strong sense thereof. It is such a sense of the Divine Presence that looms in front of us when we daven. We may never have had the experience of an overt Divine encounter personally, but the Avos did.
Our "sense of the Divine" does not originate within ourselves, rather it has to come to us via the avos. Rashi makes this point when he interprets Shemos 15:2, based on the Mechilta, as follows: "this is the G-d of my father and I will exalt Him – I am not the source of this kedusha; it is something established for me from the days of the Avos."
Every tefillah must start with the sense of "omeid lifnei haShechinah" or it is not tefillah at all. This sense is accessible to each and every one of us because we are able to tap into "The G-d of Avraham, the G-d of Yitzchok, and the G-d of Yaakov", and if we fail to note that our tefillah is invalid.
Yerushalayim is the location for Divine service, and Chevron is the repository of the Avos. We cannot properly engage in Divine service without our connection to the Avos. Therefore, as soon as the spiritual cornerstone of Yerushalayim was laid via the akeidah, the beracha of the "G-d of our forefathers" was similarly symbolically established in Chevron.