Keeping His Power Under Control
Stick and Luke provide the biggest character contrast in The Defenders. The old blind man has seen his share of bad, and he acts accordingly, while Luke refuses to succumb to easy solutions. After witnessing the gruesome beheading of Hand leader Sowande, Luke is indignant at the implication that Stick is just going to get rid of the body. "Hand related or not, that was a homicide, man," he says.
Just before the last remaining member of The Chaste tries to kill Luke, he tells him that when the real fight happens, he needs to not hold back. "I'm not here to do damage. I take no joy in watching people get hurt," he tells Stick about how he plans to proceed whenever The Hand showdown actually happens. Luke is well aware of his capabilities, but there's also a part of him that knows he has to self regulate - otherwise, he runs the risk of becoming a weapon in the same way that Kilgrave used him in Jessica Jones season 1.
After Matt, Luke, and Jessica have been captured, Luke knows that there's no way they can get out of the police station without doing something bad -- and he's willing to accept the punishment for it. By now, he's fully committed to destroying The Hand. Even though he should let Misty in on this, he pleads with her to let him do what he does best and help her, and by default, the people of Harlem. In the very first episode, before he gets to take his first steps of freedom, Foggy Nelson compliments Luke on his restraint saying, "You made it through a prison stint without throwing a single punch."
Innocent Lives Above All Else
Luke has no problem bending rules or roughing up criminals like Turk in Trouble & A Pair of Dice, but he absolutely takes issue with those he believes to be innocent being used as cannon fodder for big time criminals. The second episode, "Mean Right Hook," marks his first meeting with Danny Rand, where Luke tries to stop Danny from hurting Cole so he can find out who hired him and why he was part of a clean up crew. After Claire officially introduces Luke and Danny, they continue to disagree about how best to go about fighting The Hand. In an exchange that captures the essence of Luke Cage's ability as a solo series to blur the lines between the MCU and the real world, Luke schools Danny about his misguided approach to taking down The Hand.
"I know privilege when I see it. You may think you earned your strength, but you had power the day you were born. Before the dragons, before the chi, you have the ability to change the world without getting anybody hurt... If I were in your shoes, I'd think twice about using that thing on people who are trying to feed their families."
The conversation does serve to make Danny think twice about his approach, and he has a similar conversation with Jessica in episode 4, "Royal Dragon." After Jessica storms out of the restaurant, Luke tells her this isn't about him and that being less selfish is a "concept [she] might want to try on sometime." Both he and Jessica got mixed up in this because they were trying to help one family. But now that they're both in the middle of something that will effect all of New York City, he acknowledges that, unlike Jessica, he's willing to "play along" if that gets him answers.
Even in the finale when everyone else has agreed that blowing up the building is the best course of action, Luke is appalled at the idea. "This is not how I fix things!" he protests. It isn't until Matt assures him that the only people in the building are them and The Hand, that Luke agrees to move forward with the explosives.
When Matt was putting the rest of the group in danger in order to protect Elektra; when Jessica was completely unbothered by a bigger picture of how dangerous The Hand could be; when Danny was blindly hunting The Hand, uncaring about who got hurt along the way, Luke Cage always stood firm in his mission to protect the innocent. Claire describes Luke in the following exchange with Misty Knight:
"Do you know what his true north is? Doing the right thing, no matter the consequence. Far as I can tell, he's finally finding his place in the world."
Luke would never call himself a hero, but the people of Harlem -- superpowered and normal alike -- know better. The fate of The Defenders (as a group and as a series) is unknown, but Luke's sense of right and wrong is just as unbreakable as his skin.
The Defenders is streaming now on Netflix.