Why did God not want the Gentiles brought in through Jewish proselytizing?
God did not want Gentiles brought in through Jewish proselytizing because He was dealing strictly with the covenant nation of Israel and setting them apart as a separated people. He never instructed Jews to proselyte or evangelize Gentiles, though He did desire Gentiles, but not by that means.
Les teaches that Israel was God's covenant people, never to intermarry with other nations or have real social contact with the pagan peoples around them. They could do business with them, but socially they were to remain a separated people. God never instructed the Jew to go out and proselyte or win the Gentiles even to their religion. God did want the Gentiles, but He did not want it by virtue of Jewish proselyting or evangelizing, because He was dealing strictly with the covenant nation He would set aside and make different. This background explains why the Jews were upset when Paul later went to the Gentiles, and why Peter struggled at Antioch in Galatians 2.