I dont know how we can prove or disprove this, but I consider his words to be the pinnacle of human teaching. He is teachings were greater than anything that came before him, and the greatest teachers since his day have relied on what Jesus said. As a teacher Jesus has never been surpassed.
McCulloch wrote:
Are all of his teachings easy to defend?
I dont know if easy is the right word. He spoke on deep topic and genuine understanding requires effort. However, all of his teachings are defendable.
For instance, McCulloch mentioned the teaching about marriage " that marriage is for life and to divorce and remarry, except in certain circumstances, is the same as adultery. Jesus teaching is absolutely correct. A life-long promise should be kept for life. The fact that not all people have followed this command doesnt make the command bad. If failure to follow a teachers instructions makes the teacher bad then we have had no good teachers in human history.
Concerning McCullochs other remarks: in context, Jesus talking being a eunuch seems to be symbolic of life-long abstinence, as opposed self-mutilation. Jesus does not command anyone to do this. He gives his followers a choice between abstinence and monogamy. His command seems right both on a moral level and on the level of what is best for society.
McCulloch wrote:
Is there anything that he could have made clearer?
I agree with Zetesis on this one. If Jesus had said that 2 + 2 = 4 then someone would have found fault with it or misused it. Teaching about the human condition requires a certain degree of vagueness so that it can be applicable to different cultures, but Jesus words seem clear enough to those who are willing to study them.
McCulloch wrote:
Did he make mistakes? Did he leave out anything important? How could he have improved as a teacher?
He left out many things. His teachings came out of what we call the Tanakh, and those writings, enlightened by the words of Jesus, help fill out our understanding. At other times we are expected to apply the general principles he taught to specific circumstances in our culture.
I can think of nothing that would have actually improved his teaching.
Understand that you might believe. Believe that you might understand. –Augustine of Hippo