The Midrash Bereshit Raba states that the world was created for the sake of Torah and Mitzvot and it is the Torah of Israel that preserves the universe. Consequently, those who study the Torah are the true prime movers of the world, and keep the earth on its orbit.

Moreover, the Talmud Yevamot 96 expounds that those whose Torah teachings and disciples survive them, continue to live in both worlds, even when their physical lives on earth are over. This is based on Tehillim 61:5, "I shall dwell in Your tents forever".
The Talmud explains that the word "forever" in Hebrew is OLAMIM which literally means "worlds" i.e.-the physical world and the World to Come.

The Torah is eternal and as long as one's Torah teachings is studied here on earth, the teacher remains alive in the physical world even after death. Thus, Rashi in Devarim Ch. 31 explains that as long as Yehoshua, Moshe's closest disciple was alive, Moshe even after death also felt very much alive.

Therefore, the Mishna in Avot Ch.1 states, "develop and set up many disciples", because through one's disciples we gain a sense of eternity and immortality. That is why in the Talmud we find many similar teachings in the name of numerous deceased Rabbis. One's Torah teachings are his passport to eternal life both in this physical world and in the World to Come.