Saint Paul does not say that baptism is not essential to the gospel. He is concerned with the administration of baptism. Saint Paul is addressing a problem that arose in the Church of Corinth where some were identifying themselves with particular ministers and causing division within the community. In 1 Corinthians 1:11-12 he writes, "For it has been reported to me by Chloe’s people that there is quarreling among you, my brethren. What I mean is that each one of you says, 'I belong to Paul,' or 'I belong to Apollos,' or 'I belong to Cephas,' or 'I belong to Christ'."Why would paul thank God that he Baptized but a few, while he preached the Gospel IF water Baptism required?
The Corinthians were adopting religious affiliations based on the minister who baptized them. Thus, Saint Paul was grateful that he had not baptized more people than he did among the Corinthians, lest they affiliate themselves with him.
It is also useful to point out that Saint Paul is using hyperbole in order to emphasize two things. First, it doesn’t matter by whom you’re baptized, and second, his apostolic role is not restricted to administering baptism but also involves preaching the gospel. St. Pauls statement, "For Christ did not send me to baptize," is hyperbolic because Jesus commanded all apostles to make disciples of all nations by baptizing them. Because St. Paul is an apostle, baptizing is part of his ministry. If Paul was not sent to baptize, then he was disobedient to his ministry since he did baptize Crispus, Gaius, and the household of Stephanas, which he tells us about in verse 14. Do we want to say that the great apostle Paul was disobedient to Jesus’ instruction?
If baptism in not essential, this is inconsistent with Pauls own writings, for Romans 6:3-4 states, "Do you not know that all of us who have been baptized into Christ Jesus were baptized into his death? We were buried therefore with him by baptism into death, so that as Christ was raised from the dead by the glory of the Father, we too might walk in newness of life."
He goes on to say, "We know that our old self was crucified with him so that the sinful body might be destroyed, and we might no longer be enslaved to sin. For he who has died is freed from sin (Romans 6:6-7)."