Spiritual deafness describes the state of those who are lacking in spirituality, whose spirit ears are not attuned to the whisperings of the still small voice of the Spirit. Similarly, spiritual blindness is the identifying mark which singles out those who are unable to see the hand of God manifest in the affairs of men. Such have ‘unbelief and blindness of heart’ (D. & C. 58:15); they are ‘hard in their hearts, and blind in their minds.’ (3 Ne. 2:1.)
(Bruce R. McConkie, Mormon Doctrine, p. 184)