Psalms of lament express our human condition. They cry for help from adversity and sorrow; or for succor from anguish and shame. They usually address God, offer Him a complaint, make a request and express trust in His deliverance.
As Christians, we all believe in God and His sovereignty. As human beings we all know how to complain and ask for things. The secret power in a psalm of lament is the last part; expressing trust in His deliverance.
Consider the problems David protests about in Psalm 27:
"...the wicked...came upon me to eat up my flesh...
an host...encamp against me...war should rise against me...
the time of trouble...
my father and my mother forsake me...
false witnesses are risen up against me, and such as breathe out cruelty."
These difficulties are more than most of us have ever known; yet in the midst of those trials He writes words of praise and trust that are unsurpassed.
"The Lord is my light and my salvation; whom shall I fear?
the Lord is the strength of my life; of whom shall I be afraid...
For in the time of trouble He shall hide me in His pavilion:
in the secret of His tabernacle shall He hide me;
He shall set me up upon a rock...
When my father and my mother forsake me,
then the Lord will take me up...
I had fainted, unless I had believed to see the goodness of the Lord in the land of the living.
Wait on the Lord: be of good courage, and He shall strengthen thine heart:
wait, I say, on the Lord."
The combination of trial and triumph is sublime. Hosanna to the Son of David. Hosanna to our God!