A.T. Robertson Commentary Acts 18:10

"for I am with thee, and no man shall set on thee to harm thee: for I have much people in this city." — Acts 18:10 (ASV)

Because I am with thee (διοτ εγω ειμ μετα σου). Jesus had given this promise to all believers (Matthew 28:20) and here he renews it to Paul. This promise changes Paul's whole outlook. Jesus had spoken to Paul before, on the way to Damascus (9:4), in Jerusalem (22:17f.), in Troas (16:9), in great crises of his life. He will hear him again (23:11; 27:23). Paul knows the voice of Jesus.

No man shall set on thee to harm thee (ουδεις επιθησετα σο του κακωσα σε). Future direct middle indicative of επιτιθημ, old and common verb, here in direct middle to lay or throw oneself upon, to attack. Jesus kept that promise in Corinth for Paul. Του κακωσα is genitive articular infinitive of purpose of κακοω, to do harm to. Paul would now face all the rabbis without fear.

I have much people (λαος εστιν μο πολυς). Dative of personal interest. "There is to me much people," not yet saved, but who will be if Paul holds on. There is the problem for every preacher and pastor, how to win the elect to Christ.