The destruction of the second Bet ha Mikdash the house of our holiness and glory and the fact that we were exiled from our land was due to the sin of Bittul Torah (abandoning, annulling the Torah) as it is explained: (Devarim 29, 23-24) “And all the nations will say: “Why did Hashem did this to this land…And they will say: For they have abandoned the covenant (Brit) of Hashem the G-d of their parents”; the covenant mentioned here is the Torah. In reality we find that The Holy One Blessed be He was lenient regarding the sin of idolatry, forbidden relations and the spilling of blood, but was not lenient regarding the denigration of the Torah as it is written: “Because they abandoned My Torah” (Jeremie, 9:12), “Me they have abandoned and My Torah they have not observed” (Jeremie,16:11). Our sages Z”L have explained this as: “I wish they had forsaken Me, but My Torah they had observed” (Yerushalmi, Hagiga, 1:6).
You will find that all that angered the Holy One Blessed be He regarding Israel was due to the Torah. For in regarding any action, no one understands its cause, quality and essence, as the one who executes it, he fully understands its essence and the reason why he did that action. Therefore, the Holy One blessed be He, who is the worker of all actions, knows that toil in the Torah is the head of all the Tikunim (repairs, corrections). He warned regarding the Torah many times, became angry at us because His Torah was abandoned. (Ramhal – Rabbi Moshe Hayim Luzzato).