The Hamlet Project

And so Horatio echoes the sense of the beginning of the play. “Who’s there?” is not so far from who comes here. It’s a subtle bookend, really. Perhaps, like the opening scene, it heightens the tension before a dramatic event.
Barnardo and Francisco become Horatio.
What’s funny is – after the sentinel’s “Who’s there?” – eventually we get to the ghost.
Immediately following “Who comes here?” – we get Osric. We get comic relief.