Paul on that occasion was employing a figure of speech known as an ellipsis ("A construction in which words are omitted but clearly understood"-Harbrace College Handbook, 1984) so as to make a point concerning the way several factions in the church in Corinth were claiming superiority over others based upon who baptized them.  The first thing that should be done in understanding Paul's meaning is to look closely at the context of the statement and then to look more closely at the statement itself.
    The context involves the church at Corinth and the tendency of some there to put unnecessary stock in the person who had converted them.  I Corinthians 1:12 defines the problem, "Now this I say, that every one of you saith, I am of Paul; and I of Apollos; and I of Cephas; and I of Christ."  In the next verses Paul is going to confront the problem in several ways.
    First, Paul asks in verse 13, "Is Christ divided? was Paul crucified for you? or were ye baptized in the name of Paul?"  These questions show that some apparently were missing the point of what baptism was, and what it was for.  Paul was asking a rhetorical question to show that division of the body of Christ should not take place over who baptized whom, rather the important thing was that all were baptized in the name, or by the authority, of one being:  Jesus Christ.
    Second, Paul thanks God in verse 14 that he did not baptize, personally, many there.  Why say this?  Because that would have had more people holding him up as being greater than he actually was.  He understood his role merely as a minister and not as a savior.  He clarifies this in verse 15 when he states, "Lest any should say that I had baptized in mine own name."  In verse 16, as in verse 14, it is shown that Paul had baptized some, but that he did not know if he had baptized others.  Why did he not know?  He didn't know so that would not be a point of contention.
    Third, Paul shows in verse 17 what his role was:  He was not a baptizer (only), but a preacher.  He was the messenger!  Had he baptized some?  Yes, therefore he must have been sent to baptize as well or else he had violated his commission.  But he was emphasizing his mission:  He was a preacher.  It did not matter who baptized these people.  What matter is that they were taught and that they were baptized by anyone in the name of Christ.  Anyone could baptize, not all could preach with authority as he did.