As was mentioned in the previous post, the children fear that Bob Ewell will attempt to harm their father in Chapter 23. Following his encounter with Bob Ewell at the post office, Atticus feels that Bob has got all of his anger out of his system. However, Atticus neglects the fact that Bob Ewell may still hold a grudge. Atticus is somewhat naive and has a tendency to see the best in people. He firmly believes that Bob Ewell is no longer a threat. Unfortunately, Bob Ewell still harbors resentment and attempts to murder Jem and Scout later on in the novel.

With regard to the given passage, Atticus demonstrates his observant, concerned nature by asking his children what is bothering them. Atticus notices that Jem and Scout are not acting normal and becomes concerned. Atticus even buys Jem a football magazine to cheer him up. Atticus's small gesture of buying Jem a present demonstrates his empathy for his son. Atticus then reassures his children that they have nothing to fear.

The children are afraid that Mr. Ewell is going to hurt Atticus, because he threatened him.  Atticus is not afriad, demonstrating that he has empathy.

Atticus does not take Mr. Ewell’s threat seriously, but the children do.  Mr. Ewell felt that Atticus made a fool out of him at the trial.  He is convinced that he can take Atticus down a peg, and the children are convinced he can do it.

Not much frightens Atticus, and he tries to keep his own problems to himself.  When he realizes that the children are afraid of Bob Ewell, he tries to tell them that Bob is all bark and no bite.

The man had to have some kind of comeback, his kind always does. So if spitting in my face and threatening me saved Mayella Ewell one extra beating, that's something I'll gladly take. (ch 23)

Atticus is able to do something he has been trying to teach his children to do for most of the book.  He can empathize with Bob Ewell.  He can walk around inside his skin.  This event also foreshadows Ewells attack on the children though.