John Calvin Commentary Acts 18:11

"And he dwelt [there] a year and six months, teaching the word of God among them." — Acts 18:11 (ASV)

He continued there a year. We do not read that Paul stayed so long anywhere else except there. Yet it appears from his two epistles that he was not only likely to suffer many troubles, but that he had also suffered many unjust and unsuitable things because of the pride and unthankfulness of the people. Thus, we see that there was no aspect of spiritual warfare in which the Lord did not wonderfully exercise him.

Also, we gather what a hard and laborious matter the building up of the Church is, seeing that the most excellent master builder spent so much time in laying the foundation of only one church.

Nor does he boast that he had finished the work, but rather that the Lord had put others in his place, so that they might build upon his foundation, as he says afterwards, that he had planted, and that Apollos had watered (1 Corinthians 3:6).