Bob Deffinbaugh wrote an article on Acts 18:1-7 at Bible.org:
It took a while to realize this, but it is noteworthy that Paul’s first significant success evangelizing among the Gentiles came at this point in time, a time when Paul was at his lowest. He was fearful, both of his safety, and of the results of his ministry if he were to stay on. This is exactly what Paul says in his epistles to the Corinthians. The praise and glory must therefore go to God, and not to men. The pronouncement of Gallio, which was of such importance to the propagation of the gospel, was not the result of Paul’s persuasive speech, for he never got so much as a single word out of his mouth. And the evangelization of the Gentiles was not the result of Paul’s abilities, for he came to them in weakness, fear, and much trembling. God does not need our human strength in order to achieve His purposes; God works through human weakness so that He receives the honor and the praise. In Paul’s stronger days, when his confidence ran higher, the results were less than spectacular. In the days of his greatness weakness, when our Lord appeared to him to comfort and encourage him, God’s greatness blessings were poured out.