Or HaChaim on Deuteronomy 32:20/אור החיים על דברים ל״ב:כ׳

1 כי דור תהפוכות המה, "for they are a generation who have reversed themselves." Inasmuch as G'd had said in the first half of this verse that He would hide His face from them, awaiting what would befall the Israelites, this implies that even if they were to turn penitent -seeing G'd would not observe this as He had stopped watching what the Israelites were doing,- He would not accept such penitence. Moses offers as the reason for such an attitude by G'd that the people have turned already from good to evil; he adds בנים ולא אמון בם, "they are thoroughly faithless children." Even if they were to repent to the point of again qualifying for the description of children (of G'd), such repentance will not endure as they are fickle and do not keep faith. As a result of such considerations G'd hides His face from them.