Pope's poem "The Rape of the Lock" is separated into five different parts (Cantos). The lines below are from Canto Two of the poem, lines 16-18:

Might hide her Faults, if Belles had faults to hide:
If to her share some Female Errors fall,
Look on her Face, and you'll forget 'em all.

Canto Two begins with Belinda on a boat on the Thames River. Pope describes Belinda as a beautiful woman with beautiful hair. One of the men on the boat with Belinda is so enamoured with her hair that he wants her locks for his own. Another passenger on the boat (Ariel) has had a premonition that something bad will happen on the boat that day and, therefore, assigns others on the boat to protect Belinda.

The meaning of the lines shown earlier describe the beauty of Belinda and women in general. The entire second stanza, where the lines appear, describe Belinda's looks. The line prior to those shown sets up the true meaning of the last three lines of the stanza:

Yet graceful Ease, and Sweetness void of Pride,

Therefore, the meaning of the three lines questioned refer to the fact that Belinda's ease and sweetness will hide any faults which her beauty covers (if women actually have any faults). In the last line, Pope is simply stating that to look upon the beauty of a woman will insure that if any faults be found they will be forgotten once one looks upon a woman's face.