In what way does the setting described in lines 1-21 suggest or foreshadow later events?
The opening lines of "The Monkey's Paw" establishes a mood of impending trouble because the little home is so isolated that the family is unprotected from any sort of trouble that could happen. But most importantly it foreshadows what will happen at the very end. Mr. White describes the neighborhood as follows:
"That's the worst of living so far out," balled Mr. White with sudden and unlooked-for violence; "Of all the beastly, slushy, out of the way places to live in, this is the worst. Path's a bog, and the road's a torrent. I don't know what people are thinking about. I suppose because only two houses in the road are let, they think it doesn't matter."
Since there is hardly anybody living in the vicinity it will seem almost a certainty that the person knocking so insistently at the door in the dead of night must be the Whites' son Herbert. If there were a lot of occupied homes and a lot of foot traffic, the chances of the knocker being a harmless stranger would be increased. But who would be coming out here at this hour other than their son?
The arrival of Sergeant-Major Morris earlier in the story emphasizes the isolation and general unpleasantness of the neighborhood.
The old man rose with hospitable haste and opening the door, was heard condoling with the new arrival. The new arrival also condoled with himself,
The description of the setting outside the house adds to the reader's impression of a dead and mutilated man standing on the other side of the front door. Outside it is pitch-dark, muddy, and cold, a fitting setting for the arrival of a horrible monster who wants to come into the warm cottage and make himself permanently at home. Both Mr. and Mrs. White are so positive it must be Herbert returned from the grave that Mr. White squanders his third wish just to be rid of the knocker.