“God does not exist.”
The central claim of atheism was a familiar one in David’s world, just as it is in ours. If there is no God, the afflicted people of God have no reason to hope. Instead, all they can look forward to is a life of pain without remedy or rescue. The corruption they see all around them wins in the end, and the wicked will get away with all their evil.
Did you know there is a Psalm that deals with the atheistic claim directly? 
In Psalm 14, we find king David fully admitting the problem of human corruption and the suffering it brings to all people, including the people of Israel. But we also get to listen in as God interrogates and refutes the apparent atheism of his deniers.

By the time this short Psalm is done, we are offered a compelling reason to have hope, corrupt and afflicted as we are.