John Gill Commentary Deuteronomy 22:21

"then they shall bring out the damsel to the door of her father`s house, and the men of her city shall stone her to death with stones, because she hath wrought folly in Israel, to play the harlot in her father`s house: so shalt thou put away the evil from the midst of thee." — Deuteronomy 22:21 (ASV)

Then they shall bring out the damsel to the door of her
father's house
For his greater disgrace, and as a sort of punishment for his neglect of her education, not taking care to instruct her, and bring her up in a better manner:

and the men of her city shall stone her with stones, that she die ;
which was the death this sort of adulteresses were put to; others was by strangling, and the daughter of a priest was to be burnt; see (Leviticus 20:10) (21:9) , which shows that this sin was committed by her after her espousals, as Jarchi and Aben Ezra note; or otherwise it would have been only simple fornication, which was not punishable with death:

because she has wrought folly in Israel :
a sin, as all sin is folly, and especially any notorious one, as this was; and which is aggravated by its being done in Israel, among a people professing the true religion, and whom God had chosen and separated from all others to be a holy people to himself:

to play the whore in her father's house ;
where she continued after her espousals, until she was taken to the house of her husband, to consummate the: marriage; and between the one and the other was this sin committed, and which is another reason for her execution at the door of her father's house:

so shall you put evil away from among you ;
deter others from it by such an example, and remove the guilt of it from them, which otherwise would lie upon them, if punishment was not inflicted; the Targum of Jonathan interprets it of the putting away of her that did the evil.