The Hamlet Project

Is Marcellus hesitating to swear upon a sword for some reason?
Is it that this swearing will be redundant after the preceding swearing in faith?
Is it that swearing upon a sword involves contact with the blade in such a way that might be painful to the swearer?
It’s possible that this is an oath Marcellus isn’t sure he should commit to before knowing what exactly the problem here is. Or maybe he’s thinking that this is one of those times when you might have to break a trust with someone in order to do something in their best interest.
I’ve had to do that and it was awful. I’d do it again, though.
I know that I will call a policeman to save you from yourself no matter how much you might hate me for it.
There are promises one just can’t keep.
Marcellus makes this one, then disappears.