Jesus defends His teaching but not His life. Why?
First He says that it is not His teaching but His Father’s teaching. Our Father gave this teaching to Jesus who gives it to us. Jesus will defend His Father and what is given to Him.
Second, Jesus knows He needs to die to save sinners. Jesus will do this when the time is right. Our Father gave Jesus authority not only to teach but to lay down His life and take it up again. Jesus will lay down His life at a time of His choosing.