The Gemara famously asks why the land was destroyed and answers that it was because they did not first make a blessing on the Torah. The passage directly states that this spiritual failure led to the loss of the land.
רָבִינָא אוֹמֵר: שֶׁאֵין מְבָרְכִין בַּתּוֹרָה תְּחִלָּה. דְּאָמַר רַב יְהוּדָה אָמַר רַב: מַאי דִּכְתִיב: ״מִי הָאִישׁ הֶחָכָם וְיָבֵן אֶת זֹאת״ — דָּבָר זֶה נִשְׁאַל לַחֲכָמִים וְלַנְּבִיאִים וְלֹא פֵּירְשׁוּהוּ, עַד שֶׁפֵּירְשׁוֹ הַקָּדוֹשׁ בָּרוּךְ הוּא בְּעַצְמוֹ, דִּכְתִיב: ״וַיֹּאמֶר ה׳ עַל עׇזְבָם אֶת תּוֹרָתִי וְגוֹ׳״. הַיְינוּ ״לֹא שָׁמְעוּ בְּקוֹלִי״, הַיְינוּ ״לֹא הָלְכוּ בָּהּ״! אָמַר רַב יְהוּדָה אָמַר רַב: שֶׁאֵין מְבָרְכִין בַּתּוֹרָה תְּחִלָּה.
Ravina says: They are punished because they do not first recite a blessing over the Torah before commencing their studies. As Rav Yehuda said that Rav said: What is the meaning of that which is written: “Who is the wise man that may understand this, and who is he to whom the mouth of the Lord has spoken, that he may declare it, for what the land is perished and laid waste like a wilderness, so that none passes through” (Jeremiah 9:11)? This matter, the question as to why Eretz Yisrael was destroyed, was asked of the Sages, i.e., “the wise man,” and of the prophets, “he to whom the mouth of the Lord has spoken,” but they could not explain it. The matter remained a mystery until the Holy One, Blessed be He, Himself explained why Eretz Yisrael was laid waste, as it is written in the next verse: “And the Lord said: Because they have forsaken My Torah which I set before them, and have not obeyed My voice, nor walked therein” (Jeremiah 9:12). It would appear that “have not obeyed My voice” is the same as “nor walked therein.” Rav Yehuda said that Rav said: The expression “nor walked therein” means that they do not first recite a blessing over the Torah, and they are therefore liable to receive the severe punishments listed in the verse.