Adam Clarke on Romans 11:8

God hath given them the spirit of slumber - As they had wilfully closed their eyes against the light, so God has, in judgment, given them up to the spirit of slumber. The very word and revelation of God, which should have awakened their consciences, and opened their eyes and ears, have had a very different effect; and because they did not receive the truth in the love thereof, that which would otherwise have been the savour of life unto life, has become the savour of death unto death; and this continues to the present day.