Matthew Henry Commentary Acts 18:7-11

"And he departed thence, and went into the house of a certain man named Titus Justus, one that worshipped God, whose house joined hard to the synagogue. And Crispus, the ruler of the synagogue, believed in the Lord with all his house; and many of the Corinthians hearing believed, and were baptized. And the Lord said unto Paul in the night by a vision, Be not afraid, but speak and hold not thy peace: for I am with thee, and no man shall set on thee to harm thee: for I have much people in this city. And he dwelt [there] a year and six months, teaching the word of God among them." — Acts 18:7-11 (ASV)

The Lord knows those who are his, indeed, and those who will be his; for it is by his work in them that they become his. Let us not despair about any place, since even in wicked Corinth Christ had many people. He will gather in his chosen flock from the places where they are scattered. Thus encouraged, the apostle continued in Corinth, and a numerous and flourishing church grew up.