It's for speed and for importance so

At a post office

-----------------

Man: I'd like to send this letter to Italy and I was wondering
what's the fastest way of sending it.
.
.
Man: Excuse me did you say 24 dollars?

Post master: Ah, yes, that's right.

Man: It's only paper.

Post master: Yes, it's just, it's for speed and for importance so.

Man: UM, I'd like to send it in a cheaper way.

.

.

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and for importance so. ?

1- What does "so" mean in this sentence?

2- What does "for importance so" mean?

Thank you