The reason Paul said he was thankful he did not baptize a great number in Corinth personally, was because he was thankful he did not ?.  You seem to have already gotten the point in your comments.  Given the divisive nature of the Corinthians, he is thankful that not all that many can pridefully declare that they were baptized by Paul.  Just the other day I told a Christian here in Kyrgyzstan that I was studied with by Tom Brown  (a guy pretty famous in my particular circle of Christians).  They were pretty impressed.  Now, I do not think that I was behaving as the Corinthians–I sure hope not, but this illustrated the potential problem.  Divisive people can base their arrogance on who they are a disciple of.   In doing hermeneutics, one of the rules for interpreting difficult passages is to ask what it CANNOT mean.  Given Paul’s other statements about baptism (Gal 3:26, Rom 6:4, etc.) we know that he cannot mean that baptism is not important.  In fact, if you look at the context of 1 Cor 1 the context is disunity, not salvation.  To be honest, the fact that he says he did not baptize such and such Christian in Corinth is not problematic except for someone who is simply trying to make trouble.

The other passage can be a bit tougher to fully explain.  I do not believe a sincere exegist would be confused by the statement about who he baptized, but an honest person might get confused about Paul’s statement about what he was sent to do.   When Paul says that he was not sent to baptize, this does need some explanation.  Surely Paul was sent to baptize (Matthew 28:18-20).  Here is how I interpret this passage.  Paul is saying that his principle assigned task from Jesus was to preach the gospel.  Actual baptizing of those converted to the gospel is secondary to his principle task. If he did not preach, then many would not be saved.  There was no alternative person with the gifts that Paul had to do what he did.  This is clear to all.  On the other hand, whether or not Paul did any actual physical baptisms was irrelevant to how many were saved in the end.  There is no gift of baptizing, as anyone can perform a baptism.  So his seemingly somewhat confusing statement is about the relative essentiality (which may not be a real word) of the two tasks.

In any case, what we can say for sure is that whether or not baptism is essential is not under discussion in 1 Corinthians 1.  In fact, even if we believe in the false doctrine that baptism is not essential (in other words, even if salvation did not occur at baptism), the interpretation difficulties would be nearly the same. In fact, the big deal that Corinthians were making over who had baptized them actually argues (weakly, but argues) FOR the importance of baptism.  It is disingenuous for people to use this passage to argue one way or another about the doctrine of baptism.

John Oakes