The reason why the "Martha" comment stopped Batman in his tracks. It was so much more than what we understood.

"You're letting him... kill Martha."

Batman doesn't lower his weapon, but he pauses. He thinks to himself, "Martha? Why would he say my mother's name?"

"What does that mean?" Batman says aloud in a modest amount of confusion.. "Why did you say that name?"

Superman wheezes, "Find him... save Martha."

Batman is more confused. He watched Martha Wayne's murder as a young boy of seven, and nothing could change this. But wait... didn't he mention something about Lex Luthor? What could he have to do with this? Then he remembers Superman pleading with Gotham's Dark Knight before the fight began that he was "wrong." This is when Batman's detective skills go into over drive, analyzing various bits of information with another being's life in his hands. But Batman still does not understand.

"Why did you say that name?" Batman demands. "MARTHA! Why did you say that name?" Superman is too exhausted to give him the information he desires. Batman wonders if this 'Superman' knew something about his mother... he'd seen so many thngs after twenty years in Gotham. Mutant crocodiles, psychotic clowns, etc... this had to be trick.

Lois barges in, pleading for him to stop as she quickly provides Batman with what he needs to make the right choice.

"It's his mother's name!" She screamed. "It's his mother's name."

Batman slowly lifts his boot off of Superman and steps back, uncertain of how to respond. But he is confident now that Luthor, one of the greatest intellects on the planet... had somehow orchestrated this.

Suddenly, it made sense why Lex found the Kryptonite... where those notes came from. He had thought it was Superman, egging him on, calling him out. Now Luthor had Superman's mother... whose name happened to be Martha as well. Of course, this similarity didn't matter... but it was the Batman's duty to protect people.

He hurled the Kryptonite away and helped Superman up while the latter explained the situation.

"They need you at that ship," Batman told him. "I'll find her."

"My mother needs me," Superman insisted, going to push past him.

"I'll make you a promise," Batman told him. He thought of his mother and how he was unable to save her and gave Superman a solemn vow, "Martha won't die tonight."

A tacit agreement was shared between the two. That Batman and Superman would ally with each other to achieve their goals. Superman would go to face Lex Luthor and stop him from whatever plot the latter had concocted— and Batman would finally let go of his assigned blame on the Kryptonian by saving his mother.

He wasn't able to stop what had happened in that alley... the day he lost everything. He was too young, too slow, and too weak.

But it was that day he swore to beat back death doing whatever it took. Batman became what he needed to be to protect life. His vendetta against Superman, engineered by Luthor, would be something he'd have to let go of— this is what it took.

This is what it would take to ensure that...

Martha would not die tonight.