Extempore reply to an invitation

Sir,
Yours this moment I unseal,
And faith I'm gay and hearty!
To tell the truth and shame the deil,
I am as fou as Bartie:
But Foorsday, sir, my promise leal,
Expect me o' your partie,
If on a beastie I can speel
Or hurl in a cartie.
Yours,
Robert Burns

Machlin,
Monday Night, 10 o'clock