Because I am with thee (dioti egō eimi meta sou). Jesus had given this promise to all believers (Mat 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 (Act 9:4), in Jerusalem (Act 22:17.), in Troas (Act 16:9), in great crises of his life. He will hear him again (Act 23:11; Act 27:23). Paul knows the voice of Jesus.
No man shall set on thee to harm thee (oudeis epithēsetai soi tou kakōsai se). Future direct middle indicative of epitithēmi, old and common verb, here in direct middle to lay or throw oneself upon, to attack. Jesus kept that promise in Corinth for Paul. Tou kakōsai is genitive articular infinitive of purpose of kakoō, to do harm to. Paul would now face all the rabbis without fear.
I have much people (laos estin moi polus). 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.