1 Corinthians 7:6

But I speak this by permission, and not of commandment (KJV)

Then: Paul wanted his readers to know these were his own thoughts. They did not come as a command from God or edict from Christ. Instead it is practical advice based on "Word-of-God" messages from Christ to Paul. Paul saw it as a way to work through and honor the one man, one wife plan. What the statement does do is give a sense of leniency. His earlier, almost harsh tone is gone. The mood is one of loving - a sense of "We're all working together here." Fee (p. 270) thinks the change means that the Corinthian problem was based on women's new place in worship. He extrapolates that although Paul agreed with the women's understanding about their new status, their conclusion that it now negated former marital responsibilities was wrong. Paul's guidelines actually have one principle - stay in and honor the relationships which were already established when you were called to become a follower.

Now: Some Christians believe that even though Paul gives this caveat, the words are biblical and must be followed. Others do not see them as mandates.

Extra source: The First Epistle to the Corinthians by Gordon D. Fee (Eerdman's 1987) online at http://books.google.com/books?id=XlBp10nUTXAC&dq=Gordon+Fee+Bible+commentator&printsec=frontcover&source=in&hl=en&ei=SwLNSu3nA4v6Mf2XlDo&sa=X&oi=book_result&ct=result&resnum=12#v=onepage&q=&f=false