Paul lives for the preaching of the gospel, and it brings him great joy. He will not allow anyone to take that joy from him, and especially the joy of doing it free of charge.
How should we regard a pastor who does not preach the gospel? Paul says, ‘Necessity [a charge or compulsion] is laid upon me’, but many cannot be persuaded to preach the gospel. They claim not to be hyper-Calvinists but they do not address unbelievers with the gospel. A pastor may regard himself as a teacher, but if he does not himself preach the gospel, he must make sure there is an evangelist in the church besides himself. You are only entitled to have a one-man ministry if you can do both, else the church must find another, or it will not grow.