Motivation: he was trying to save his wife from being accused of witchcraft and being hung.Plot: He has many people try to help his stop the accusers from saying his wife had witchcraft behavior. Also, wanted to stop the one time affair he had with Abigail.
Comparison: In real life John Proctor had seven kids with Elizabeth. However, in the Crucible book he only had six children with her. Another difference is John and Abigail didn't have an affair in real life, but in the book they did.