I think the desert here is a symbol of that which of old was void of all God's good things, I mean the Church of the (432) Gentiles, and the river by the desert that cleanses all that are bathed therein is a figure of some cleansing spiritual power, of which the Scriptures speak, saying, "The movements of the river make glad the city of God." And this means the ever-flowing stream of the Holy Spirit welling from above and watering the city of God, which is the (b) name for life according to God. This river of God, then, has reached even unto the desert, that is the Gentile Church, and even now supplies it with the living water that it bears.