In Leviticus 26:44, after describing the hardships that the people would suffer while fulfilling the precepts that God had given them, the text says that even those living in the Diaspora remain in covenant with God. God does not despise or end relationship with them. In the Midrash on Leviticus (Sifra) the Sages explore this verse by asking the question: what remains of all the beautiful gifts from God that Jews have received which sustain their covenant with God? And the answer is: Only the Torah (Bechukotai, parashah Bet, chapter 8).
The Temple of Jerusalem was destroyed, the land of Israel remained for two thousand years in the hands of different empires, and Jews were spread throughout the world. Only the Torah remained with Jews and it was the study of its text that maintained the identity of the people of Israel and their covenant with God.
The Talmud (Berachot 61 b, Sanhedrin 14 a; etc) tells us that on multiple occasions the Sages risked their lives by teaching the Torah, defying the Roman decree that prohibited such action. The Roman oppressors knew the Jewish desire for freedom, which had caused them to rebel against the empire on multiple occasions, was inspired by the Torah. They knew that the identity of the Jewish people was preserved by their devotion to the Torah.
One of the best-known cases among those who gave their lives for teaching the Torah is that of Rabbi Chanina ben Teradion (Avodah Zarah 18 a). He was condemned by the Romans to die by being cremated in the flames of the Torah scroll he had used to teach publicly. As he was being consumed by the fire, his students asked him: Teacher, what do you see? He replied: I see the scroll burning, but its letters are flying to the heavens.
In many moments of Jewish history its sacred texts were destroyed, such as the burning of the Talmud in Paris in 1244, in 1553 in the Campo dei Fiori in Rome, and in other places in other times. But the letters could not be burned. They lived on into the present and were reflected again and again on paper and on parchment. That is why the day on which the annual reading cycle of the Torah is over is of such joy and happiness: because faith is greater than destructive fire.
Chag Sameach!