"O, w'ad the power some giftie....."

What are those lines of poetry (and who was the poet who wrote them) that go something like "O, w'ad the power some giftie g'e us, to see oursel's as others see us."

And what exactly is a "giftie" or whatever it is, anyway?

Tidepool

It's Robert Burns' "To A Louse". "Giftie" is gift. The original and it's translation can be found at the link below.