Why does God speak in dreams and visions?

“Behold, in this you are not right. I will answer you.

 God is greater than man.

 

"Why do you contend against him,

    saying, ‘He will answer none of my words’?

 

"For God speaks in one way,

    and in two, though man does not perceive it.

 

"In a dream, in a vision of the night,

    when deep sleep falls upon men,

    while they slumber on their beds,

 

"then he opens the ears of men,

    and terrifies them with warnings,

 

"that he may turn man aside from his deed,

    and cut off pride from man;

 

"he keeps back his soul from the Pit,

    his life from perishing by the sword."           

Job 33:14-18