The other verse in this Psalm that sticks out to me is verse 7. David (hiding in the cave from King Saul) starts out by talking about hiding in the Lord's shelter and in this verse it seems to me that he is making a declaration about his own heart. The hiding king states: my heart is steadfast, O God, my heart is steadfast...I will sing, yes, I will sing praises! To me he is declaring that no matter how bleak his outward circumstances are looking he will remain steadfast, trusting in the Lord and he's even gonna sing!
I think it might read more like this if I was penning the psalm I will sing? yes...I will sing. Singing does not seem to match the situation does it? Here is the future king - and he knows it! - hiding from a mad man yet determined to stay hidden in God and to keep his heart steadfast before Him...and even thinking about singing in the cave!
He then encourages himself and tells his soul to wake up! and give thanks. He did not thank God for the cave. He did not thank God for riches, peace or health. He thanked God for the things in his life that remain even while hiding in a cave. Think about it - he certainly did not feel rich, there was no peace in the natural, and he was not too concerned about getting out to the gym that morning or eating a well balanced diet. It was far less than perfect circumstances by our American standards.
So he began to thank God for some of His constants....His lovingkindness and His truth. Two things that never change or fail in the face of life's circumstances. So maybe we feel hidden in a cave brought about by life's harsh circumstances; let us rejoice today in His truth and His mercy that never fail!