Psalm 88 aches with dark despair. It begins with a cry for God's help, but ends with a sad confession, "You have taken away my companions and loved ones. Darkness is my closest friend" (88:18). Though we don't know the exact nature or extent of the psalmist's pain, we do sense that he has mostly given up hope. "I am as good as dead," he laments (88:4).
I find it striking that Psalm 88 includes virtually no words of reassurance. Nowhere does the psalmist add parenthetically, "But you are the Lord of mercy and compassion," or anything else like this. Most psalms of lament include words of hope. But not Psalm 88. Here we find dark despair.
Yet, even in the "lowest pit" (88:6), the psalmist keeps on talking with God. He hasn't stopped reaching out to the Lord, even though he has no apparent confidence that this will do any good. By putting his prayer in writing, the psalmist encourages us to keep in dialogue with God no matter what. God is able to handle our despair, our doubt, our anger, and anything else we might throw at him. In fact, I believe God has put this psalm into the canon of Scripture, in part, to give us permission to tell him anything. It's one of those psalms that encourages us to pray with "no holds barred."