The author says, "Christ was not sent as a teacher of morality...."

Some clarification might be helpful: Jesus did teach for some time before he went to the cross. He taught not only about who he was and the meaning of his ultimate sacrifice; he also taught many things about what new life in him entails with respect to our aspirations and attitudes and behavior, pointing with great love to the potential for our blessedness, fruitfulness, and joy, to God's glory.

"If you know these things, blessed are you if you do them." - John 13:17 ESV
"By this my Father is glorified, that you bear much fruit and so prove to be my disciples." - John 15:8 ESV
"These things I have spoken to you, that my joy may be in you, and that your joy may be full." - John 15:11 ESV