What does Jesus help Joel understand in chapter 13 of The Bronze Bow?

According to Matthew 5:17-20 Jesus said that he came, not to destroy the Law, but to fulfill it. In other words, his earthly ministry was the completion of the prophecies set out in the Old Testament. As Jesus is the son of God, he's able to explain certain complicated passages of the Law in a way that Joel, and countless other Jewish followers, are able to understand. What is particularly astonishing about this for Joel is that Jesus is not a rabbi, someone learned in the Law. Yet nonetheless he's able to provide insights into that Law like no one else can.

Joel's not just confused about this because of Jesus' humble background, but also because his message of peace contradicts his—Joel's—assumption that the Messiah will be a great warrior king who will drive the Romans out of Israel by force of arms. Jesus' clear teaching of the Law has forced Joel, like so many others, to reflect deeply on his entire religious worldview.

What does Jesus help Joel understand in chapter 13 of The Bronze Bow?

When Joel and his sister visit Daniel and Leah, Joel tells Daniel that he has been waking up early in the mornings to listen to Jesus when he talks with the fishermen. When Daniel asks Joel if he thinks Jesus will help them, Joel tells Daniel that Jesus helped explain several specific points of the Law that have always puzzled him. Daniel is shocked that Jesus, who is only a carpenter, can understand more than the scholars that teach Joel. Joel then proceeds to tell Daniel that Jesus has the ability to take complicated parts of the Law and explain them in understandable terms. Joel also mentions that Jesus's messages are similar to his father's but somehow seem to go beyond. Joel then encourages Daniel to come listen to Jesus with him and invites him to come along on his next visit. 

In The Bronze Bow, how does Jesus help Joel?

When the novel begins, Joel is a young scholar being readied to become a Rabbi and teacher at the synagogue. His meeting with Daniel inflames his patriotism, and he starts to ignore his studies and follow the path of a warrior, despite being unsuited for it. He is not as directly affected by Jesus as Daniel and Thacia, and he continues to desire conflict until Daniel, of all people, convinces him that his studies will be more helpful to the cause than his sacrifice.

Finally [Simon] spoke. "[Jesus] will never lead us against Rome, Daniel. I have given up all hope of that."

The quiet words had the force of a blow. Daniel had his answer at last. Joel had tried to tell him, and Thacia. Even Jesus himself.
(Speare, The Bronze Bow, Google Books)

This is the point when the reader truly understands how Jesus affected Joel. Instead of fighting his sermons, Joel was able to embrace them more fully than Daniel, because he understood the content of them, not simply the emotion. Joel knows that violent revolution will not be successful, and as Jesus preaches, they must work to change the hearts and minds of the people -- including the Romans. For Joel, returning to his studies is his way of embracing the teachings of Jesus, since he will serve in a similar role to teach and educate.

In The Bronze Bow, how does Jesus help Joel?

Joel had been recruited into Rosh’s resistance by Daniel. At the time Daniel was not fully aware of Rosh’s selfish nature; it was only when Rosh refused to participate in Joel's rescue that he acknowledged his true character. Daniel was also attending some of Jesus’ teachings, which pointed to the error in his method of seeking freedom and vengeance. Jesus also taught him values such as love and inclusion, which were distant qualities in Daniel’s world.

Joel shared similar sentiments and, according to the two boys, violence was the answer to the Roman problem. Joel was later arrested by the Romans, and two of his colleagues died during the rescue mission. The experience confirmed Jesus’ teaching that violence was not the answer. After the ordeal, Daniel pleaded with Joel to go back to school, suggesting that their movement would employ a different strategy in future. Therefore, not only did Jesus save Joel, but he also saved Daniel.