I suppose I should feel bad for spoiling this unexpected scene in a movie full of them, but I don't. There's not much plot in this movie to spoil, anyway.
The movie doesn't judge Joe for being a contract killer. It doesn't let him off the hook or venerate him as a vigilante. It lets him be in the job, almost as though it's a job like any other. The job is horrible, but so is life, so there's a balance to it.
The movie doesn't judge you either or treat you like a dummy (too many movies think we need the plot endlessly repeated). It gives you just enough info, then expects you to keep up. And you do, in part because the movie doesn't have much in the way of distractions, but mostly because the movie picks you up and carries you along. Doesn't explain. Just carries you and drops you off at the end.
Which is Joe's job, if you think about it.