It isn’t a joke as such, in the sense of a double meaning. It’s just an amusing situation. The angel has been sent on an assignment. He has spent time saving this person’s soul, then discovers it’s the wrong person.
It’s a germ of an idea that might make an amusing short story, but doesn’t work as a single panel.
Comics I Don't Understand 
Alternative jokes:
“J-O-H-N. With and ‘H’! If I’ve told you once, I’ve told you 316 times!”
“Michael kept looking for the right Jon. After 316 tries, he figured this guy was good enough.”
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Angel got the wrong man. Meanwhile, Jon-the-really-bad is pursuing is evil ways unchecked.
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‘His’ not ‘is’ – stupid cheap keyboard.
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It isn’t a joke as such, in the sense of a double meaning. It’s just an amusing situation. The angel has been sent on an assignment. He has spent time saving this person’s soul, then discovers it’s the wrong person.
It’s a germ of an idea that might make an amusing short story, but doesn’t work as a single panel.
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My real name being Nick, and me being over 60, I get this sort of thing all the time: angels bothering me because they think I am THAT old Nick.
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Tell ’em you’re Old ST. Nick. Big difference!
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