The ultimate cause of all spiritual depression is unbelief. For if it were not for unbelief even the devil could do nothing. It is because we listen to the devil instead of listening to God that we go down before him and fall before his attacks. That is why this psalmist keeps on saying to himself: “Hope thou in God for I shall yet praise Him…” He reminds himself of God. Why? Because he was depressed and had forgotten God, so that his faith and his unbelief in God and in God’s power, and in his relationship to God, were not what they ought to be. We can indeed sum it all up by saying that the final and ultimate cause is just sheer unbelief.