Book 4 of Mere Christianity, entitled "Beyond Personality: or First Steps in the Doctrine of the Trinity" delves into some great theological doctrines. Lewis is intent on explaining that is all about a new kind of life. "If Christianity only means one more bit of good advice, then Christianity is of no importance. There has been no lack of good advice for the last four thousand years. A bit more makes no difference. But as soon as you look at any real Christian writings, you find that they are talking about something quite different from this popular religion. ...Now the point in Christianity which gives us the greatest shock is the statement that by attaching ourselves to Christ, we can "become Sons of God."