Why did the Corinthians reject Paul even though he loved them?
The Corinthians rejected Paul because they preferred Peter, who had been with Christ, over Paul, who never was. Although Paul loved them abundantly and was willing to spend and be spent for them, they turned against him and said they would not listen to him.
Les explains that Paul had turned his back on everything in order to take the Gospel to pagan, ungodly, immoral Gentiles. In verse 15 Paul says he would very gladly spend and be spent for them, though the more abundantly he loved them, the less he was loved. Les points out that the more Paul loved those Corinthians, the more they turned against him and said they would not listen to that man; they would listen to Peter instead. After all, Peter was with Christ, but Paul never was. So their rejection came even though Paul loved them and was willing to be spent for them.
And I will very gladly spend and be spent for you; though the more abundantly I love you, the less I be loved.