My Lutheran pastor used to say that if God let us know what was coming we'd want to run and hide.
A good friend compared the Christian life to a journey down a tunnel. God gives us "headlamps" that don't let us see more than we can handle.
The sea used to be a symbol of untamed evil -- that's why the evil critters in Revelations come up out of the sea. So "no more sea" is a way of saying that the source of evil has been shut down!