This promise occurs in a chapter drenched with thoughts of God's good intentions toward his people; his willingness to make a covenant with them and fulfill his promises to David. Of course the picture cannot be understood as a literal description of future events. The language of metaphor is required in order to represent what God intends. Trees have no hands to clap with, nor do mountains have vocal chords. But the imagery speaks unmistakably of a state accord in creation. The fraught relationship between the non-human environment will no longer be and a state of mutual joy will preside.
I'm busy working on my blog posts. Watch this space!