The joke reading of this line is not obvious. That is, as the set up for the joke that’s coming, it is not obvious. Nor is the joke, when it comes. Without examination, the line just seems like someone paying respects. If it were another character commending duty to this lordship, it might draw no notice at all. But as it is, it’s Osric, so of course this line is heard by Hamlet and Horatio as self praise instead of an expression of duty to a prince.
They hear it as Osric honoring himself – honoring his own honoring, as it were.