Why did Eddie's father save Mickey instead of killing him or letting him drown for what he attempt with Eddie's mother?

Ruby teaches Eddie the lesson of forgiveness by revealing the truth behind Eddie's father's death. "Things are not always what they seem," (137) Ruby preaches as she explains the reasoning behind Mickey Shea's assault on Eddie's mother. She explains that Eddie's father died in an act of loyalty, which is complicated for Eddie to understand considering the murky moral circumstances of Eddie's father's fight with Mickey. However, Ruby's alternative perspective on these events eventually gives Eddie the ability to forgive his father.

Ruby teaches Eddie about the importance of contextualizing people's actions. Eddie is naturally furious to learn that Mickey Shea tried to assault Eddie's mother, but Ruby urges Eddie not to categorize Mickey as a good man or a bad man. In that moment, Mickey was just desperate and broken, and once he realized how low he had sunk, he wanted to die. Just as Eddie's father was able to put aside Mickey's heinous actions and save his old friend's life, Ruby uges Eddie to do the same.