"As a deer pants for flowing streams, so pants my soul for you, O God." Well, that's a nice sentiment, isn't it? But why? Verse 3 tells us (and verse 10 brings the same thought) "My tears have been my food day and night, while they say to me all the day long, 'Where is your God?'" It sounds like the writer is in deep turmoil and persecution, from some source we don't know. Verse 4 tells of more pleasant days, wishing he were back there. Oh, the misery!
Verses 5 and 11 both ask, "why are you cast down, O my soul?" -- in this way, the psalmist is examining himself, looking at the inner turmoil and searching for the source of it. The fond memories of worship in verse 4, contrasted with taunts in verses 3 and 10, seem to be the cause of the anguished emotions.
Facing our troubles honestly, and learning from them, is much better than simply stumbling over the same issues, or avoiding them because they're painful. Here, the writer is treating his inner self as a third party, asking himself, "what's going on?" and seeking more clarity. That's a good lesson.
But as well, the writer is correcting himself, saying "Yes, that is trouble -- but still, hope in God; for I shall again praise him, my salvation and my God." He couldn't come to the second place without having gone to the first, could he? Neither can we.
The last few days, when I've been worried about something, I've gone back to this psalm, first admitting why I'm troubled, and giving up my desire to control the part that is truly out of my control. Then I have reminded myself that this is a slight and temporary thing compared to knowing and being loved by God. It's been helpful. Can you try it too?