The core idea that Avraham, as the first and root of Yisrael, sets the pattern that 'draws after it' everything that follows is stated directly in Gevurot Hashem 8:30, which explains that the vision shown to Avraham at the covenant was like the moment of a person's birth that determines all that follows — since he is the rosh and ikar of Yisrael, the beginning carries the power to draw the whole course of the nation after it.
The Ramban (Bereishit 12:6) grounds this same principle in the rabbinic teaching that 'whatever happened to the Avot is a sign for the children,' explaining that the Torah dwells at length on the travels and travails of Avraham, Yitzchak, and Yaakov precisely because these events teach what is destined to recur for their descendants — not mere historical narrative but a template for the future.
Several passages from Gevurot Hashem and Netzach Yisrael develop the theme that Avraham is the yesod and hatchala of the world and of Yisrael specifically: Gevurot Hashem 9:36 states that Avraham, being first, is called 'echad' and merited to be rosh, nasi, and av hamon precisely because he is the beginning; Gevurot Hashem 7:18 ties this to his emunah, through which he became the shoresh and yesod of all Yisrael; Gevurot Hashem 5:2 cites the midrash that the world was created for Avraham's sake, making him the even pinah of all creation; and Netzach Yisrael 59:19 adds that Avraham is the ikar metziut ha'olam, the reishit habriah, upon whom everything else is tafel.
The pesukim themselves bear out that Avraham's selection was bound up with his role as transmitter to his descendants: Bereishit 18:18-19 states that God singled out Avraham so that he would instruct his children and posterity to keep the way of Hashem, and Bereishit 26:2-5 records that the blessing to the nations continues through his seed specifically 'because Avraham obeyed Me and kept My charge.'
Likkutei Sichos 5 Lech Lecha develops the same 'maaseh avot siman lebanim' idea beyond mere sign: the sicha explains that Avraham's own actions, such as his descent to Egypt, are themselves the cause that empowers what later happens to his descendants, so that every spiritual descent becomes a preparation for a later ascent.
Tiferet Yisrael 20:1-3 situates Avraham's unique standing in his connection to the Torah itself, teaching that Avraham recognized his Creator at age three and was singled out, more than Yitzchak and Yaakov who only received from him, to fulfill the whole Torah through the elyon intellect that corresponds to the Torah's own nature.
Beyond the theoretical plane, Mishneh Torah, Foreign Worship and Customs of the Nations 1:3 records how this 'first' role played out historically, describing Avraham traveling from city to city and kingdom to kingdom proclaiming the one God, gathering thousands who became the people of his household — a concrete expression of being the hatchala from whom everything else follows.
Other sources round out the picture of what is drawn after Avraham's beginning: the Sforno (Bereishit 12:2) reads 'veheyeh brachah' as Avraham becoming a source of blessing through his own growth in wisdom and teaching; Netivot Olam, Netiv Gmilut Chasadim 1:5 identifies gemilut chasadim as Avraham's defining midah, citing both his keeping of Hashem's mishmeret and his charge to his household; and Kad HaKemach, Guests 1 and Peninei Halakhah, The Nation and the Land 7:10 describe his hospitality as rosh hamachzikim, running after guests to do chesed, a pattern he set for his descendants.
Netzach Yisrael 8:2 frames Yisrael's distinctiveness among the nations in terms of fundamental division among all existing things, supporting the broader claim that the nation founded by Avraham stands apart as its own category from the start.
Pirkei Avot 1:1-2 and Sifrei Devarim 343:8 show the chain of transmission and selection continuing forward from the Avot: Avot records how Torah passed from Moshe through the generations, while Sifrei notes that only once 'pesolet' had been separated out through Avraham and Yitzchak did a generation (Yaakov's) emerge entirely without it, mirroring the idea that each generation builds on, and refines, what the first established.
Rav Kook (Ein Aya, Berakhot 1:77), Rav Kook (Ein Aya, Berakhot 1:175), and Rav Kook (Ein Aya, Berakhot 1:176) extend this foundational role into the universal plane, describing Avraham as the one who proclaimed the one God as Master over all creation and as the shoresh hadaat for Yisrael's nationhood, whose purpose from its very inception was to bring blessing and tikkun to all humanity.
Rav Eliezer Melamed (Peninei Halakhah, The Nation and the Land 1:6) and Rav Eliezer Melamed (Peninei Halakhah, Family 8:1) connect this foundational status to the very first command given to Avraham, Lech Lecha, to go to the land, from which the nation's capacity to reveal Hashem's word to the world would flow, and to the first individual mitzvah of brit milah, showing how the start of Avraham's path shaped what would follow for his descendants both nationally and individually.