I’d like you to avoid violence if at all possible, but if they harm Grace in any way, kill them all.
There’s something chilling in listening to Finch utter those words and seeing Reese’s subtle reaction to it. Finch has always been that good guy, going so far as to disappear after the Machine sent the POI team on a killing mission in Person of Interest Season 3 Episode 20.
His faith was clearly shaken, but the strong character that he is, he was able to convince Reese to follow him and not the computer. He’s formed that bond of friendship that extends beyond their work, and it was clear during Person of Interest Season 3 Episode 21.