The quote identified in this question is used in this poem to describe the white sheets as they hang on the washing line and dry outside, which the speaker in this poem remembers playing with when she was little. Note how she describes her memory of amusing herself with these sheets:
High scented walls there were flapping white
when I was small, myself.
I walked between them, playing Out Of Sight.
Simpler than arms, they wrapped and comforted--
clean corridors of hiding, roofed with blue--
saying, Your sins too are made Monday new...
The quote starts off with a metaphor used to describe the sheets. For the small, young speaker, they represented "High scented walls" rather than sheets, that she could use to hide between and play with. The personification is used to endow these sheets with human qualities as the speaker remembers being "wrapped and comforted" as she walked between them outside, and presumably the wind blew them around her. The way she remembers that this "comforted" her indicates this was a profoundly positive memory. In fact, this is supported by the way that she associates this memory with the voice saying she is forgiven for her "sins." The personification in this quote therefore is used to highlight the happiness of the memory the speaker has of playing with these sheets, and suggest how she found playing with them comforting and, to a certain extent, liberating. This of course is something the speaker uses later on in the poem as a contrast to identify the various restrictions women face and as a symbol for women themselves in their progress through life from free and aspiring to limited and acquiescing.