David is in middle of describing the beauty of nature in a profound way.Why is he suddenly saying here smack in the middle of the story "how great are your works" ?
The reason for that is because the greatest thing in the world is that a person goes out to work every day which many times seem like darkness (ערב) and he can change the world to be a better more spiritual place to see god's work something that none of nature can do and that is where the statement of

'מה רבו מעשיך ה

belongs more then anywhere else of that chapter .
We are not here in this world to be living on the top of a mountain or a retreat all our lives.We are not here to be "workshop junkies " .
The 7 days of pesach are our spiritual retreat to connect to the abstractness of God, to our being and we remind ourselves twice a day by kriat shma of that spritual high but god put us here to take that deep connection and bring it into our daily lives which many times look so far from him.