This chapter is a pivotal point in Daniel's growth and maturation. He and Thacia travel to visit Leah, with Thacia in disguise as Joel so Joel can gather information. During this trip, they are waylaid by Roman guards, and Daniel's rage almost gets them killed; Thacia shows him that they need to pick their battles instead of fighting blindly. Her influence on Daniel is subtle but is paid off later, as she explains the philosophy of love instead of hate:
"You see, Jesus has made me see that we don't need to wait for God to care for us. He does that now. Every one of us. Jesus says that God sees into our hearts and loves us. If everyone understood that—every man and woman--"
"Would that rid us of the Romans?"
"Suppose -- the Romans too could understand?"
(Speare, The Bronze Bow, Google Books)
After this, they visit Leah, where Daniel's anger at Marcus, the Roman guard who visits her, is reignited. Then Daniel and Thacia share a moment of mutual attraction, which affects their friendship.
The key points in this chapter are Thacia explaining the love of all men to Daniel, which he initially rejects. Since all men are worthy of love, at some level, it should be possible and even necessary for Daniel to love the Romans. Daniel takes this in but refuses to implement it until the last chapter, when he shows kindness to Marcus; this is the payoff of Thacia's passing on the teachings of Jesus.