Musar על ישעיהו 5:24

Also, through this [(laxity in Torah study)] the idolators grow in strength over Israel, as we find in the Midrash (Eichah Rabba Pethichta) on the verse (Isaiah 5:24): 'As straw [Esav] will consume a tongue of fire [Jacob].' When will the straw consume the fire? 'When they [Israel] despise the Torah of the L-rd their [Israel's] root will be like rot.' The 'merit of the fathers' will not avail them."