Who was Yitzchok? Was he merely a bridge between Avrohom and Yaakov? Or was he as much of a “founding father” of Judaism as Avrohom and Yaakov.
What does it mean to be a “founding father” or “mother” (Sorah, Rivka, Rachel and Leah)? When a tree is planted and the owner of the tree realizes the tree will grow in an undesirable direction, it is very simple to rectify the problem in the first couple of years of the tree’s life.
So too in Judaism. When Avrohom discovered Hashem and started the process of the Jewish nation any act he did would have consequences for thousands of years. Any test which he and the other “fathers” and “mothers” were given was something that was neccessary to ensure our survival as a people.
Avrohom’s primary characteristic was Chesed—lovingkindness. This was expressed by the expansion of his message. Thousands of people followed Avrohom and Sorah to hear their message of belief in Hashem and the idea that life has purpose.
Yitzchok’s primary character trait was Gevura—strength of conviction; discipline. While the role of Avrohom was in building, Yitzchok’s role was in strengthening the building—internalizing the message of his parents.
Hashem’s communication with Avrohom was totally different from the way it was with Yitzchok. For example, while Hashem told Avrohom to bring Yitzchok up as an offering, He never directly told Yitzchok—Yitzchok only heard it from his father. But Yitzchok’s strong conviction allowed him to impicitly trust Hashem.
Over the course of his life Avrohom dug many wells. In the time of Yitzchok most of these wells were filled in by the Phillistines. Yitzchok redug these same wells. Thus we see his reaction was never to lose hope, but to see adversity only as a temporary setback. This is metaphorical of the Jewish role after destruction of our Temples and other setbacks we have suffered as a nation.
Just as Avrohom’s quality—willingness to sacrifice all that is dear for Hashem—enabled so many Jews throughout the generations togive their lives for Judaism, similarly Yitzchok’s strong conviction has enabled us to come back from so many setbacks.
What happenned to the thousands of followers Avrohom and Sorah attracted? When these people heard the message of Avrohom and Sorah, it struck a chord in them. However, when they saw what Yitzchok had to go through, they decided they would “keep” what they had learned from Avrohom and Sorah, but the next step was too much for them. This is why Avraham is considered “father of all nations”, while Yitzchok is exclusively a Jewish father.