Why is "Let the dead bury the dead." relevant with repsect to the theme or symbolism in this book?

In other words, let Tom Robinson "bury" Bob Ewell as an act of poetic justice, and the incident will be taken care of; in this way, Boo Radley with his "shy ways" will not be exposed to the gossip and cruelties of the public. The town can "move on" from the repercussions of the trial as all the injustice connected to it will finally end. The dead will take care of the dead, and the living will go on living in their own ways. Otherwise, it would be like killing a mockingbird to bring Boo to court.

Atticus finally understands the wisdom of Sheriff Tate and agrees with him.