The Midrashim suggest an unusual transformation occurred to Avraham during Akeidas Yitzchak. In the Torah (Bereishis 22:2) Avraham is told to bring Yitzchak to the “land of Moriah.” The Midrashim offer different interpretations for the meaning of this name. Yalkut Shimoni (Shir Hashirim) explains,
דבר אחר מוריה תמורה, אברהם נעשה כהן גדול תמורת שם בן נח שנאמר לא יחליפנו ולא ימיר וגו’
Another reading: Moriah as in Temurah (exchange), Avraham became a kohein gadol (The High Priest), in place of Shem the son of Noach.
This interpretation in the Midrash explains that Moriah derives from the similar sounding word: Temurah, which means to exchange. The meaning then is that Avraham was substituted as the new kohein gadol in place of Shem, Noach’s son, the former pre-Torah kohein gadol. This needed to take effect in order for Avraham to bring his son Yitzchak as a korban.
While this notion requires overall explanation, Rav Silver focused on a technical question: Why did Avraham need to be a kohein gadol in order to sacrifice Yitzchak, and not just a regular kohein? A regular kohein can also bring sacrifices, so why wasn’t being transformed into a regular kohein sufficient for Avraham?
Other midrashim do speak of Avraham being transformed into a regular kohein, with no mention of becoming a kohein gadol. For example, one Midrash (Yalkut Shimoni, Va’erah) says,
והעלהו שם לעולה אמר לפני הקב”ה וכי יש קרבן בלא כהן א”ל הקב”ה כבר מניתיך שתהא כהן הה”ד נשבע ה’ ולא ינחם אתה כהן לעולם
“Bring him there as an olah sacrifice” – [Avraham] said to the Holy One Blessed is He, “is there a korban without a kohein?” The Holy One Blessed is He replied “I have already appointed you to be a kohein”
In this Midrash the same tradition of Avraham becoming a kohein is recorded, but here Avraham is transformed into a regular kohein, not a kohein gadol.
Even the need for a kohein is unclear, because prior to the Beis Hamikdash, the service was done by the firstborns, and Avraham was the firstborn in his family, according to another Midrash (Bereishis Rabbah 38), so he should have been fit for the service simply by being a firstborn, with no need to be a kohein at all?
Rav Silver suggested the answer to this question is that since God had chosen the place for Akeidas Yitzchak, it had a law similar to that of the Beis Hamikdash, which was also chosen by God. Unlike the bamot – the individualized places of sacrifice which existed before the Beis Hamikdash, and where firstborns did the service, Akeidas Yitzchak was to be done in a place selected by God, like the Beis Hamikdash, and so it required a kohein.
But this still only explains the need for a regular kohein, why was a kohein gadol needed?
Rav Meir Simcha of Dvinsk, one of Rav Silver’s rebbeim, in his work on the Torah Meshech Chochmah (Bereishis 21:17), explained the need for a kohein gadol derives from the tremendous sanctity of the mountain upon which Akeidas Yitzchak occurred, which was equivalent to that of Yom Kippur. Rav Meir Simcha derives this because the angel who spoke to Avraham had to make his voice heard from afar, but could not actually step onto the mountain. This reflects the level of holiness in the Beis Hamikdash on Yom Kippur, when even angels couldn’t step near, only the kohein gadol could go inside. Therefore Avraham needed the status of a kohein gadol in order to be present during the worship of Akeidas Yitzchak.
Rav Yosef Rosen, the Rogatchover Gaon, another of Rav Silver’s rebbeim, was asked this question (Teshuvot #72) and he answered based on halachic concern. A regular kohein who is an onen – i.e. one who has lost a relative until the day of the burial, is prohibited to offer a sacrifice, but a kohein gadol is permitted to offer sacrifices even as an onen. The reason is that the kohein gadol does not involve himself with the burial of even his relatives, and so he may continue working in the Beis Hamikdash even after losing a relative. Since Avraham was about to sacrifice his son, he would have a halachic problem that he was about to become an onen, and as such would be prohibited from concluding Akeidas Yitzchak. Therefore some midrashim suggested that Avraham was considered, not a regular kohein, but a kohein gadol, and as such could conclude the service he had begun.
But the Rogatchover was asked (Teshuvot #101) that this contradicted his own ruling in his commentary Tzafnas Paneach on the Rambam (Laws of Nazir, ch. 7), where he had distinguished between which sacrifice the kohein gadol onen is bringing. The Rogatchover had ruled that a kohein gadol who is an onen can only bring someone else’s sacrifice, meaning he can offer it on their behalf. But he is prohibited from bringing his own sacrifice, even though he’s a kohein gadol. If so, this modification of the law regarding a kohein gadol onen would also negate his answer as to how Avraham could bring Yitzchak. Since this was Avraham’s sacrifice, even for a kohein gadol it is prohibited?
The Rogatchover responded to the questioner that in his commentary on the Rambam he had already pointed to a number of exceptions to his stringency, cases where the kohein gadol could sacrifice even his own korban. For example, if the kohein gadol already sanctified this animal as a korban before his relative passed, he could still bring it. The only prohibition was to sanctify new animals as an onen. Another exception was if the obligation for this sacrifice was pre-existing before the relative had died. Again in that case the kohein gadol could bring this sacrifice. Both of these exceptions would apply to Avraham the kohein gadol, since Yitzchak was already sanctified before Avraham became an onen, and the obligation was prior to becoming an onen, so he could conclude the sacrifice.
While in Morocco, Rav Silver heard a class on the Zohar, and was inspired to think about this topic in a new way, which provided a new answer to the internal contradiction in the Rogatchover’s writings. Based on the Zohar’s language, Rav Silver argued that Yitzchak was not Avraham’s personal sacrifice, but rather was God’s sacrifice, similar to a communal sacrifice. Yitzchak was not Avraham’s property, and so he could not be sacrificed as an offering from Avraham. Rather God was demanding Avraham bring a sacrifice, but the property owner of Yitzchak should be viewed as: either he owned himself or he was owned by God.
The Rogatchover then could have answered this questioner differently, that although he prohibited a kohein gadol onen from bringing his own personal sacrifices, in the case of Akeidas Yitzchak this was not Avraham’s personal sacrifice, but rather God’s sacrifice, and so a kohein gadol onen could bring it.
Expanding on this theme, Rav Silver suggested the original idea that ownership when it comes to sacrifices, does not follow the same criteria as financial ownership. Meaning there can be times when someone brings a sacrifice which is not considered their personal sacrifice. There can be situations in halacha when one is offering a sacrifice which is considered for God to the extent that the human owner is not viewed as the owner. The notion of financial ownership does not necessarily translate fully into ownership for sacrificial matters.
A related halachic issue which involves Akeidas Yitzchak is the ram which Avraham ended up offering instead. Pirkei Avos (5:6) states that this ram was created in the six days of creation, which would mean it was over 2000 years old when Avraham sacrificed it. Some commentators understand this to mean that God thought of the idea of creating this ram during the six days of creation, though it was only born much later, a few years before Akeidas Yitzchak (see the discussion in Tosafos Yom Tov to Avos.)
But if we understand this Mishna literally, Rav Silver asked a halachic question. The Mishna (Parah 1:2) states that older animals are not permitted to be brought as a korban, because it’s not respectful to the concept of korbanot to bring an old and feeble animal. Korbanot deserve a young, strong, healthy animal. The Mishna defines older, according to the most lenient position of Rabbi Meir, as at most five years old. So how could Avraham bring a ram which was millenia old, if even over five years old is considered too old for a korban?
Rav Silver resolved this based on the position of the Korban Aharon, which is quoted by the Tosafos Yom Tov (Parah, ibid.) and the Mishneh Lemelech (Laws of Issuri Mizbeach 2:6). The Korban Aharon argued that the prohibition on bringing older animals was not absolute and merely reflected the general consensus that older animals are oftentimes disrespectful to be brought as a korban. But if one does bring an older animal it is not invalid. This position suggests that if an older animal is healthy it can be brought as a korban, it would be an exception to the general ban on older animals. If so, the ram Avraham found may have been healthy, though it was millenia old, and still kosher to be brought as a korban.
It is worth noting that the Vilna Gaon (commentary to Parah, ibid.) strongly rejects the position of the Korban Aharon, arguing that we do not give reasons for the halacha and then change the halacha accordingly. According to the Vilna Gaon an older animal would be strictly prohibited to be brought as a korban.