I wish to thank you for this excellent summation for why water baptism is necessary for salvation! I could have looked all the Scriptures up of course, but this was concise and perfect. You see, sir, I began to feel the need to explain what my beliefs were on Facebook. I have several dear friends who believe something I feel extraordinary. They are Bereans - believers that Paul brought the Gentiles a separate message from the Jews! They believe nothing is necessary for salvation except belief that He died. It's so different from any concept I've heard about that I can't adequately describe it, except to say they believe that Paul's gospel "to the Gentiles" to be the definition of rightly dividing Scripture. So I used your summation- with full credit.
You might also be interested in The Gospel of the Circumcision and the Uncircumcision.