למה תאמר יעקב ... נסתרה דרכי מה' ... (ישעי' מ-כז)
Through Yeshaya HaNavi, Hashem reminds Klal Yisroel to stay away from idol worship and preserve their purity so that when the time for redemption comes, the nation will be ready.
The Yalkut Shimoni writes how on Har Sinai, Hashem said to Klal Yisroel, “Bring Me a guarantee that you will keep the Torah.” The Jews offered, Avraham, Yitzchok and Yaakov, as their guarantors but Hashem did not accept them. Avraham could not be accepted since he had questioned Hashem with the words "במה אדע" - “How shall I know” (Bereshis 15:8) - meaning that Avraham Avinu did not fully believe that Hashem would fulfill His promise to give him the Land of Israel. Yitzchok was not accepted as a guarantor because he loved Esav, and Hashem did not accept Yaakov because he had said "נסתרה דרכי" - “My way is hidden from Hashem” (Yeshaya 40:27). Ultimately, Klal Yisroel asked that future generations be accepted as guarantors for the Torah and Hashem accepted with the stipulation that as soon as Klal Yisroel no longer keeps the Torah, the guarantors will be made to pay the price. We understand why Hashem did not accept Avraham and Yitzchok, but why was Yaakov refused?
R’ Yaakov Ashkenazi zt”l gives a simple answer. While we surely understand that questioning Hashem and associating with the people we shouldn’t, may be a disqualification, we must also understand that giving up is also a disqualification. Chazal teach us: “Even if a sharp sword is on our necks, a Yid should never give up hope.” Truly a lesson for the ages.