What is all this juice and all this joy? (line 9)
Our speaker doesn't believe the natural world is something humans should just look at and say "Ooh, how pretty" and move on. Yes, it should be enjoyed and celebrated, but here he tells us that it should also be contemplated. Not only should we observe closely, but we also ought to think about what we observe and how that relates to the world (which, in our speaker's, case has a lot to do with his Christian beliefs).