How did John MacArthur first become interested in doctrine?

How did John MacArthur first become interested in doctrine? In this video he tells his story. He has edited a new systematic theology of the Christian faith with Crossway called Biblical Doctrine: A Systematic Summary of the Christian Faith. John MacArthur is the pastor-teacher of Grace Community Church, as well as an author, conference speaker, president of The Master’s College and Seminary, and featured teacher with the Grace to You media ministry. Since completing his first best-selling book The Gospel According to Jesus in 1988, John has written nearly 400 books and study guides, including Our Sufficiency in Christ, Strange Fire, Ashamed of the Gospel, The Murder of Jesus, A Tale of Two Sons, Twelve Ordinary Men, The Truth War, The Jesus You Can’t Ignore, Slave, One Perfect Life, and The MacArthur New Testament Commentary series. John and his wife, Patricia, live in Southern California and have four married children: Matt, Marcy, Mark, and Melinda. They also enjoy the enthusiastic company of their fifteen grandchildren.