Jack: Don't. It's not real. Look, you want to push the button, you do it yourself.
Locke: If it's not real, then what are you doing here, Jack? Why did you come back? - Orientation
Here's a song involving John and Jack's argument down in the hatch at the end of Orientation, to the tune of Pinocchio's I've Got No Strings. Jack finally gives in, but real faith doesn't come until much later...
I’ve Got No Faith
Jack: I’ve got no faith in destiny.
I only trust what I can see.
You have faith, but luckily,
There is no faith in me.
Desmond was clearly cracked.
Nothing’s gonna happen, John.
This hatch would stay intact
Even if we all were gone.
John: You’ve got no faith? Then tell me, Jack,
Why did you bother coming back?
Trust the film. This job’s for two.
I know there’s faith in you.
Sayid: He has no faith, so let him be.
This argument is boring me.
Step aside, and I will do
What Jack refuses to.
Kate: You have no faith. I’m with you there.
But this is giving me a scare.
Just in case the tape is true,
I’d push if I were you.
Jack: John, you’re a silly sheep.
Desmond didn’t have a clue.
John: Why won’t you take the leap?
I believe, but I need you.
Alarm: BEEP! BEEP! BEEP! BEEP!
Jack: (pushes button) There’s still no faith in me!