וְאֵלֶּה תּוֹלְדֹת יִצְחָק בֶּן־אַבְרָהָם אַבְרָהָם הוֹלִיד אֶת־יִצְחָק׃
“And these are the generations of Yitzchok, the son of Avraham, Avraham begot Yitzchok.” (Bereishis 25:19)
On this pasuk, the midrash (Midrash Rabbah 63:1) comments, “And these are the generations of Yitzchak ben Avraham. It is written, ‘The father of a tzaddik is very happy (two forms of the word “happy” are repeated in the pasuk, “gil” and “yagil”)... happiness after happiness.’ (This happens) when a tzaddik is born. It is written in Yeshayahu, ‘And it was in the days of Achaz (a very wicked king) etc. the malachim (angels) said before Hashem, “It is a shame that Achaz became king!’” Hashem replied to them that, ‘He is the son of Yusam (a very righteous king) so I cannot remove him... happiness after happiness (occurs) when a tzaddik begets a tzaddik.’”
The Zera Shimshon asks firstly, what difficulty did the midrash have in understanding the pasuk: “And these are the generations of Yitzchok, the son of Avraham, Avraham begot Yitzchok,” that the pasuk, “The father of a tzaddik is very happy,” answers? And, secondly, how did it resolve this problem?
To answer this question, let us first understand what is the exact reasoning of the melachim who were very distressed that Hashem made Achaz the king, and what was Hashem’s reasoning that He rejected their argument and made him a king.
The Zera Shimshon explains these two opinions in light of two other disagreements (machlokosim):
We find the first machlokes in the Tosfos Yom Tov (Eidius, perek 2, mishna 9) who quotes a Tosefta that children benefit from the merits of their fathers in Olam Hazeh (this world) only until they are able to have their own merits — meaning, until their bar mitzvah. After that, “they are on their own.” The Yerushalmi argues and holds that a child reaps benefits from their father’s merits even after they are responsible for themselves and are able to have their own merits.
The second machlokes is concerning the Gemara in Sanhedrin 104a that even a wicked father benefits from his son’s merits. The Maharsha explains the reason for this is because even though that the father is a rasha, since his child changed — it must be that he contributed to this, so he is also entitled to some reward. The Iyun Yaakov argues and explains that even though the father has no hand in the good deeds of the son, a father and son are really one entity — and since the son deserves a reward for his good deeds and the father is a part of him — he also gets rewarded.
The Zera Shimshon explains that there is really only one underlying principle in these two disputes; if a father and son are one entity or not. The Iyun Yaakov who holds that a wicked father benefits from his righteous son — because they are two parts of the same being — holds like the Yerushalmi that a father’s merit will benefit his son, even after he is bar mitzvah for the same reason — since, they are both one entity.
On the other hand, the Maharsha who holds that the reason that a wicked father benefits from his righteous son is only because the father helped his son to get where he got to — holds that the son can benefit from the father only until the bar mitzvah — because it is only until that age, that the father’s chinuch is apparent in him.
There are also two more practical differences between Maharsha’s understanding and Iyun Yaakov’s understanding.
According to the Maharsha, a wicked son will not benefit from his father’s good deeds, since the parents’ chinuch didn’t work; but according to the Iyun Yaakov — since they are both in essence one entity — the wicked son will benefit from the father’s righteousness.
Another difference is that — according to the Iyun Yaakov — a father who is a tzaddik benefits from the good deeds of his son, because they are one entity. However, according to the Maharsha, a father who is a tzaddik does not get extra sechar for his child’s good deeds. (The Zera Shimshon (Shimshon Pincus) explains the reasoning for this, but, unfortunately, I didn’t understand it, so I can’t write it.)
Two more facts are needed to understand Zera Shimshon’s explanation of the midrash. Firstly, Achaz was the son of Yusam, who was a tzaddik, and Achaz’s son was Chizkiyahu, who was also a tzaddik, and Achaz became king when he was twenty years old.
The second fact is that a person is only punished by the bais din shel Ma’ala (the Heavenly Court) after he is two years old. Therefore, Achaz was considered a rasha only after he became the king.
Putting it all together, the Melachim argued that a father and son are two entities — like the opinion of the Maharsha and Tosefta — and, therefore, the merits of his son, Chizkiyahu, who was a tzaddik, could not help Achaz to have a place in Olam Habah since he was a rasha. For Achaz’s own good, they wanted Hashem to take him away from this world, before he was 20 years old and would become a king. Like this, he would not yet be judged as a rasha and the merits of Chizkiyahu, who was only nine years old — but already showed signs of great righteousness — would help him to have a portion in the World-to-Come.
Hashem argued back that the halacha is like the Iyun Yaakov and Yerushalmi that father and son are one entity and, therefore, even though that Achaz was a rasha, the merits of his father, Yusum, prevented Me from having him die early, and the merits of Chizkiyahu, his son, will enable him to have a portion in the World-to-Come.
In light of the above, we can understand the midrash was bothered by the phrase, “Avraham begot Yitzchok,” that seems to be superfluous, since it is written in the previous phrase that “Yitzchok was the son of Avraham.” The midrash’s answer to this question is that the extra phrase is teaching us that the father isn’t only an external cause for the son to be born, but the father and son are really one entity, and the proof of this is Achaz — who benefited both from his father’s righteousness and his son’s — even though that he, himself, was a rasha!