The Psalms are King David’s autobiography, a spiritual record of God’s delivering him from dark places. For example, when he fled from Saul into a cave, he wrote:
Have mercy on me, my God, have mercy on me,
for in you I take refuge.
I will take refuge in the shadow of your wings
until the disaster has passed.
David had his ups and downs and suffered from acute depression at times, and I expect he read and reread the psalms he penned when he fell into new dark places.
We too have our ups and downs, but when darkness arrives, we become unable to remember the times God delivered us. That’s why we need to record our triumphs, so we can read and reread them when disheartening times come, as surely they will. I myself have an “I Can Trust Him Journal” in which I record my deliverances as they occur and read and reread them when afflictions and tragedy strike anew.