Deep Calls to Deep

I have never been able to wrap my mind around that statement. I have really never been able to "get it".
Psalm 42
 As a deer pants for flowing streams,
  so pants my soul for you, O God.
 My soul thirsts for God,
  for the living God.
 When shall I come and appear before God?
 My tears have been my food
  day and night,
 while they say to me all the day long,
  “Where is your God?”
 These things I remember,
  as I pour out my soul:
 how I would go with the throng
  and lead them in procession to the house of God
 with glad shouts and songs of praise,
  a multitude keeping festival.
 Why are you cast down, O my soul,
  and why are you in turmoil within me?
 Hope in God; for I shall again praise him,
  my salvation and my God.
 My soul is cast down within me;
  therefore I remember you
 from the land of Jordan and of Hermon,
  from Mount Mizar.
 Deep calls to deep
  at the roar of your waterfalls;
 all your breakers and your waves
  have gone over me.
 By day the LORD commands his steadfast love,
  and at night his song is with me,
  a prayer to the God of my life.
 I say to God, my rock:
  “Why have you forgotten me?
 Why do I go mourning
  because of the oppression of the enemy?”
 As with a deadly wound in my bones,
  my adversaries taunt me,
 while they say to me all the day long,
  “Where is your God?”
 Why are you cast down, O my soul,
  and why are you in turmoil within me?
 Hope in God; for I shall again praise him,
  my salvation and my God.
(Psalm 42 ESV)

I don't have some deep explination for this scripture, I'm just soaking it in and claiming that I shall again praise him.

shaina