Inside, Walter says he's told Peck how to do it, and now he must not! You can imagine if Peck agrees with him. Walter says, "You'll never be able to live with the consequences," but he's not talking about people dying. And then he gives Peck the abridged version of the story of him taking Peter from another universe. "And since then, not a day has passed without me feeling the burden of that act," he says.
And while the tactical team storms the building, Walter sits down to tell Peck something he's never told another soul: "Until I took my son from the other side, I had never believed in God," he says, but now he figures that he betrayed God by taking Peter, and everything that's happened since has been God punishing him: "So now I'm looking for a sign of forgiveness. I've asked God for a sign of forgiveness. A specific one, a white tulip." Is that what he was talking about when he told Olivia he was waiting for something? You're not going to tell your son that he's from another universe unless you get a white tulip? Peck points out that tulips don't bloom this time of year, but Walter didn't specify "in spring" or anything. Besides, "he's God," points out Walter. "And if God can forgive me for my acts than maybe ... it's in the realm of possibility that my son, possibly, may be able to forgive me too." I'm not sure where Walter is getting that, since one of the central tenets of Christianity is that God will forgive absolutely everything that one is truly sorry for.
Peck sounds like Walter must have used to sound, as he leans forward and says, "God is science. God is polio and flu vaccines and MRI machines and artificial hearts. If you are a man of science (Dr. Jack Shephard?), then that's the only faith we need."
And we watch as the boots of the tac team make their way down the hallway, like JUST HOW FAR AWAY did they set up? Nice that they sent Walter in alone to talk to a guy who they think killed twelve people whilst being so far away from the suspect that it's taken them five minutes of running and THEY'RE NOT HERE YET.
Fortunately, this gives Walter time to give Peck a warning, that there will be repercussions if he pulls Arlette from that car: "You don't know how things will be changed by your actions, but they will." It's not our place to adjust the universe, Walter says, adding, "And you will never be able to look at her again without knowing that, just like every time I look at my son." And she'll never be able to look at Peck again without saying, "OH MY GOD WHAT HAPPENED TO YOUR BODY" and running screaming from the room.