1 Corinthians 10:2

And were all baptized unto Moses in the cloud and in the sea (KJV)

Then: Jewish believers in Christ knew intuitively that they were a continuous part of God's plan and now were personally and fully blessed by the Lord's spirit through baptism (immersion). The Gentile Corinthians didn't have that connection. Paul had to make one and he does. It's a quid pro quo action. The Corinthians gave God their belief in him and his son. God gave them his promised inheritance, salvation through Christ. Being baptized is the connection. Like the Israelites following Moses, both Jews and Gentiles following Christ moved into a new promised land, a place in the Lord's kingdom (Baker, p. 142). Claimed and loved by the jealous God of Israel, the Corinthians need to ensure that all their actions keep them within the laws of Christ (Dunn and Rogerson, p.1331).

Now: Paul's idea is not seen as being new or different. Believers accept it as a fact, a solid comparison or analogy heard so many times that few take time to think about it.

Extra source: Cornerstone Biblical Commentary 1 Corinthians (William Baker), 2 Corinthians (Ralph Martin & Carl Toney), ed. by Philip Comfort. Carol Stream: Tyndale House Publishers, c2006.
Eerdmans commentary on the Bible by James D. G. Dunn, John William Rogerson on line at http://books.google.com/books?id=2Vo-11umIZQC&pg=PA1353&lpg=PA1353&dq=1+Corinthians+9+commentary&source=bl&ots=5QeQaYWrMS&sig=S5F3KcA_TvNMyywqRiimySoUYtc&hl=en&ei=QqHPSouICIWj8AaZxqyABA&sa=X&oi=book_result&ct=result&resnum=8&ved=0CBkQ6AEwBzgU#v=onepage&q=1%20Corinthians%209%20commentary&f=false