Would you please explain the concept of great rabbis being able to manipulate nature. For example, how was Moshe able to command the Sea to open before the Israelites? Or how were other great rabbis able to do such miraculous things, even if on a lesser scale than the parting of the Sea.
You may be familiar with the concept in Judaism referred to as “gematria” where the Hebrew letters have numerical values such that otherwise hidden connections between words may be revealed through their numerical values. One such example addresses your question:
One of the names of G‑d is “Elokim” (spelled alef, vav, lamed, hey, mem). The Hebrew word for “Nature” is “HaTeva” (spelled hey, tet, vet, ayin). Interestingly, the name Elokim, which is the name associated with G‑d’s rulership over Creation, has the gematria numerical equivalent as “HaTeva” (81). This reveals that everything that we view as Nature or the forces thereof are really outer, physical manifestations of the underlying creative force of G‑d in Existence.
Those who are truly connected to G‑d, then, such as the greatest of righteous rabbis, can actually suspend or alter the normal functioning of nature by “tweaking” its source.
However, the answer is even deeper than this, and the example you bring of Moshe “parting” the Sea is especially instructive. The Midrash (Shemot Raba 21) notes that the Sea did not actually comply with Moshe’s command. Rather, G‑d intervened on the Jewish People’s behalf and only then did the Sea actually split.
Rabbi Chaim Atar, referred to as the Holy Ohr HaChaim notes (Ex. 14:27) that this is in distinction to other examples where a righteous rabbi commanded water to make way and the waters did his bidding:
In one case, Rabbi Pincahas Ben Yair was on his way to redeem Jewish captives (Chulin 7a). He came across a river and ordered it to part so he could complete his important mission and mitzva. The river replied: “Regarding your mission, you might succeed and you might not. But I am certainly fulfilling my mission by allowing these waters to flow through me.” The rabbi responded, “If you don’t part for me, I’ll see to it that no water will flow here till the end of time!” Upon this, the river parted to enable the rabbi to redeem the captives.
In another case, Joshua ordered the waters of the Jordan River to part for the Jewish People’s entry into the Land of Israel. The waters stopped in their course and piled up in a wall upstream to enable the Jews to pass into the Land (Joshua 3:15-17).
The question is, why in these cases did Nature comply with the will of the righteous but for Moshe, it required direct divine intervention? Particularly since Moshe was certainly greater than Rabbi Pinchas ben Yair, and also greater than Joshua who was only Moshe’s disciple!
The Ohr HaChaim answers that since, according to Jewish sources, the Torah serves as a blueprint for Creation, a rabbi who is completely subservient and connected to the Torah can have the plan redrawn at his bidding at any time. The essential difference between Moshe at the parting of the Reed Sea and these later rabbis is that, at the Reed Sea, Moshe had not actually received the Torah yet.
Accordingly, what enables great rabbis to manipulate Nature is: 1] Their connection to G‑d Who is the force behind everything and 2] Their connection to the Torah which dictates the guidelines of how G‑d’s creative power will be manifested in Creation.