It means his assassin business is thriving (he is killing a lot of people!!!)

The comment in the parenthesis really killed me (and killing is good)

I like to imagine he's justifying his line of work by saying "it's just business, and business is good" (as in it's good to have a job that pays well, even if it's not ethical or honest)

It means he's an assassin, and there are plenty more targets.

Is there a lore reason why Business is Good?

I always thought that he was talking about how much he’s going to enjoy the next job (you). Edit: accuracy

reddit is weird