The Lord says, "I'm about to do a new thing." This new thing will be so overwhelming that they will be able forget what things had been like. As examples of how radical the new thing is, the Lord asks them to imagine a wilderness, "I'll make a path through it." The Lord asks them to imagine a desert, "I'll put a river in that desert for my chosen people."
But, not just for them. The Lord then tells them the reason for these overwhelming gifts, gifts that would be as welcome and life-saving as a path through a wilderness or a river in a desert: "So that they might declare my praise."
God makes gifts to us so that we can acknowledge those gifts; that is, so we can witness to others what God can do, what God does do. We aren't supposed to clutch our gifts to ourselves. The ancient texts taught this, and now modern people are demonstrating that it is true.
One example is Social scientists build case for survival of the kindest. Their results indicate that generosity toward others turns out to be good for us.