Things are not going particularly well for David; we know this because in verses 9-11, he talks about those who are seeking his very life. In spite of all this, there is David; not complaining, not cowering in fear. Instead, he chooses to praise the Lord, and cling to Him. David's choice was not contingent upon his set of circumstances, or his surroundings. He chose to seek the Lord earnestly (vs. 1), to bless Him and "lift up his hands in [God's] name" (vs.4). He meditated upon the Lord, even in the watches of the night.
It's kind of like Jeremiah 17:7-8 says: Those who trust in the Lord are blessed, and will be like a tree that's planted by streams of water. It's "...roots spread out by the river", despite the heat; this tree is still green and bearing fruit regardless of it's surroundings, because of where it's planted. Physical safety and water were not the source of David's confidence; God was. King David drew from an endless stream of hope and strength.
It doesn't matter what my circumstances are, it doesn't matter whether or not I seem to be in a desert place; if my roots are spread out by the river of Living Water, I have all I could ever need. All I have to do is trust and obey right where I am at the moment. David could not control his circumstances, but he could control himself; he chose to do what was right. Seek God in the good times and the hard times, and let God take care of the rest.
