Or HaChaim on Deuteronomy 32:37/אור החיים על דברים ל״ב:ל״ז

1 אי אלוקימו Israel will begin to ask at such a time: "where is their G'd, the Rock that used to be its refuge?" Even though the deeds of the Israelites are not such that they qualify for G'd's intervention on its behalf, the people will come with a complaint against G'd although they observe only a small part of G'd's Torah. They do at least feel that their G'd ought to take them under His wings. They are conscious that they suffer all kinds of afflictions on account of the Lord being their G'd. They allowed themselves to die for the sake of the holy name of G'd, even. This is why they (the survivors) look to G'd hopefully, i.e. צור חסיו בו, "the Rock in whom they sought refuge."