Although the baptism of the Ethiopian is merely a baptism with water he can continue on his way to the south to await the power of the Holy Spirit at the ends of the earth. This return to Ethiopia is quasi a converse pilgrimage of the nations.
The new dispersion of the Jews among the nations is opposed to the OT prophecy of an assemblage on the Zion. Paul has to be converted to this new understanding of diaspora. He abandons the idea of an assemblage of captured Christians in Jerusalem and goes himself as a captive into exile. With his arrival in Rome a new Babylonian captivity of salvation is realized.