Rashi explains in his commentary: All the worlds and heavens, angels and Paradise, the earth and all the creatures that fill it, everything was created for one purpose: Torah and Torah students. There is no other reason. The nations of the world live in our merit and for our sakes, so that each one of us can sit and study Torah while they engage in keeping the physical world functioning. That’s the whole caboodle. Without Torah, the world is superfluous and there is no point for its existence.
When G-d created His universe, He instituted another law, a kind of caveat, which conditions the existence of the world on the Jewish people receiving the Torah and studying it. As the prophet says in G-d’s name: “If not for My covenant day and night — I would not have put in place the laws of heaven and earth.” (Jer. 33:25) This means that if G-d’s covenant of the Torah is not being studied day and night, then the heaven and earth will return to its original state of darkness and void.
Rabbi Chaim Volozhin writes this even more explicitly in his book Nefesh HaChayim (page 227) : “The truth is that without the slightest doubt, if the entire world would be without even one second of Jews studying and meditating in Torah, in that second all the worlds, including both upper and lower, would be destroyed. All would be empty and darkness G-d forbid…”
Rabbi Moshe Levi says on this that if it would happen that at a particular moment there is only one Jew studying Torah, the reward for that Jew (for the moment he is studying) would be the same as for one who saved every person living in the world as well as all those who will be born in the future.
This reality gives us an answer to two interesting questions:
1) Why was the earth created round so that when it is dark on one side of the world, it is daytime on the other?
Why didn’t G-d make the world flat, so that everyone can go to sleep at the same time and rise to the new day at the same hour? Rabbi Levi Assoulin in his book Bnei Levi gives this interesting explanation: If the world would have been created flat, at night time everyone would be sleeping and there would be no one to uphold the world through his Torah study. But since the world is round, then when those on one side are sleeping, it is daytime on the other side and people are studying Torah there.
The world works like a well-functioning machine. If it continues to function day and night, the energy that keeps it going — Torah study — must also keep going day and night around the clock.
2) Why is Purim the only holiday that was ordained for 2 different days — either the 14th or 15th of Adar, depending on where one lives?
Rabbi Meir Mazuz writes in his book Asaf Ha-Mazkir (“Purim”) this interesting reason: “Because people get drunk on this holiday, there is a concern that the world will remain without Torah study on this day. Therefore they ordained two different dates for this holiday so when some Jews are celebrating the holiday on one date, other Jews will devote themselves to Torah study.”
The answer to this question became clear when the students of the Mirrer yeshiva fled from a Europe on fire to the safety of Japan, and the Trans-Siberian railway was their route of escape. The rescue of these students to the Far East provided a powerful energy wave of Torah study to offset the Torah study being lost in Europe.