'Dull of Hearing' in the Bible

For the heart of his people is made fat, Their ears are dull of hearing; Their eyes, too, have they closed, Lest some day their eyes should perceive, And their ears should hear, And their heart should understand and turn, And I should heal them.

Concerning him I have much to say, and much that is hard to make clear to you, because you have grown dull of hearing.