Why does Paul not want believers to remain untaught?
Paul does not want believers to remain untaught because he wants them to be a well-taught people, well read in the Scriptures, and not ignorant of the mystery, the secret God kept hidden until revealing it to Paul. The church has failed by not teaching people, leaving many unable to say what they believe.
Les explains that Paul is driving home the truth that believers are to be a well-taught people. He does not want believers to be untaught, and Les says this is where the church, generally speaking, has failed miserably: it has not taught its people. Les maintains that you can ask the average Roman Catholic, Episcopalian, Baptist, Methodist, or others what they believe, and most cannot tell you, because nobody teaches them. Paul also does not want Gentile believers ignorant of the mystery, or secret, that God had kept in His own mind until He revealed it to the Apostle Paul. Therefore believers should be well read in the Scriptures and not ignorant of this revealed secret.