How does Les answer the question of whether his ministry is legitimate without formal credentials?

Les explains that Paul faced the same complaint, especially from the Jewish community, that he was not one of the Twelve and had not walked with Jesus three years like Peter. Paul answered that the Corinthians themselves were his work in the Lord: if he was not an apostle to others, he was to them, because they had been saved out of abject idolatry only through his ministry. Les applies this: when people ask who he thinks he is, a layman without education standing up to teach the Word, his proof of the pudding is umpteen people saved out of especially abject sinful backgrounds, coming out of darkness into the light of the Gospel. He says the Lord has honored what they are doing by seeing so many people come out of darkness and into the light of the Gospel.