Why does Les believe Luke was not a Gentile?
The conviction is that Luke had to be a Jew, or at least half a Jew, because Scripture emphasizes that only Jews wrote this book by the inspiration of the Spirit. The oracles of God were committed to them, so Luke was not a Gentile.
Les teaches, when going into the book of Acts, that Luke was not a Gentile. He is convinced Luke had to be a Jew; if he wasn't a full Jew, he was at least half of one. The reason given is that Scripture makes a point of the fact that only Jews wrote this book by inspiration of the Spirit. This fits Paul's point that the Jews had much advantage every way, chiefly because unto them were committed the oracles of God.