Doc isn't familiar with the song so unfortunately the reference is lost on him. He had millions of tracks he had missed to catch up on and he would likely never get through everything even if he listened to a few new songs everyday.

He thinks 'speed dial' means John Constantine can call upon an angel at any time and somehow Doc is doubtful of this. The man is prickly, reckless, overcompensatingly cocky to mask the fact he does not think highly of himself. Even if they could be summoned, like dogs, it would take the patience of several angels, divine beings that they might be, to be willing to come at Constantine's beck and call.

"Perhaps we are in a place where angels fear to tread. If there is a God up there he cares not for us," Doc says simply with a sigh and a tilt of his head, hands going to his hips as he turns to double check down the sides of buildings they pass. John is probably out of earshot with Doc not raising his voice so he may be talking to himself. It's fine. He's used to that too.

God may not have saved John Henry Holliday from a fate of his own making, but he would have saved Raylan from his father. And John from his. He should have. There is no mercy or grace in subjecting children to that.