Tony's first answer was right
O wad some Power the giftie gie us
To see oursels as ithers see us!
It wad frae mony a blunder free us,
An' foolish notion:
What airs in dress an' gait wad lea'e us,
An' ev'n devotion!
In the glossary, "giftie" is defined as a diminutive of "gift," which clears up the sentence.
A rough translation might be "Oh, would that some Power the gift give to us to see ourselves as others see us." "Some Power" is the giver of the gift.
The whole poem can be found here, based on Burns observing the course of a louse working its way across a fine lady's hat.