What did the Judaizers say to undermine Paul?
The Judaizers said Peter spent three years with the Lord, Peter was their spokesman, and Peter was the one they would listen to. They thereby exalted Peter's experience and authority above Paul's apostleship, seeking to undermine Paul's credibility and redirect hearers to Peter.
Les explains that the Judaizers' tactic was to elevate Peter: they said Peter spent three years with the Lord, Peter was their spokesman, and Peter was the one they would listen to. Les notes that Paul especially defends his apostleship throughout the Corinthian letters, more than in his others, because everywhere he went the Judaizers raised this claim. Paul faced satanic opposition from every possible direction as soon as he began his ministry among the Gentiles. He grew weary and almost despaired of life itself, feeling that just as he was getting the gospel off the ground, everything fell in on him. Les reminds us Paul was as human as we are and despaired even of life from his sickbed. Other factions also said things, but the Judaizers' specific words were about Peter's three years with the Lord and Peter being the one to listen to.