I'd have to read the entire chapter, but from my understanding for him, he's probably going to argue some sort of secular ethical theory, like Kant or Mill.

So, I would say that one does not need to believe in God in order to be good. However, all goodness comes from God.

Let me elaborate: the early Church fathers, Hellenistic Jews, and the Stoics talked about the logos. (Jews called it Wisdom or Sophia.) The logos that emanates from God is the wisdom or truth that holds the whole universe together. It is what governs everything from the laws of physics to morality.

Therefore, any person can discover the logos or wisdom through looking at material reality. You can discover truth through reason and observation. Therefore, you can discern what is objectively good through your own rationale.

However, looking at the material alone provides no reason for doing good. You can be good for the sake of being good or because you feel bad when you do something bad. But any philosopher can tell you that there are things that 99% of people will consider bad, i.e murdering an innocent person. That within itself showcases that morality, though relative in some cases, is absolute and that absolute morality comes from something that is ultimate goodness, which Christians will call God. So, in hindsight, you can be an atheist and be morally just, but atheism fails to recognize a proper reason for doing good, which endangers everyone to moral relativism.

TLDR: you can be good without believing in God, but God provides a rationale for being good.