Deuteronomy 17:2

If there be found among you in one of your cities that the Lord your God will give you a man or woman who doth what is evil before the Lord your God in transgressing His covenant,

If there be found among you … After mentioning the case of an asherah near the altar — something which is out in the open, in plain sight of everyone — Scripture now turns to admonish us concerning a private individual who commits idolatry.

breaking a covenant means the opposite of fulfilling it.

IF THERE BE FOUND IN THE MIDST OF THEE WITHIN ANY OF THY GATES WHICH THE ETERNAL THY G-D GIVETH THEE. I have already explained that when he speaks of the ordinances he mentions first the judgment to be executed upon the idols or their worshippers. He states [here] within any of thy gates which the Eternal thy G-d giveth thee, not to imply that this law applies only in the Land of Israel, since one who worships idols outside the Land is also liable to stoning. The purport thereof is rather to state, “if the matter be found in one of the distant cities which G-d will give you when He will enlarge thy border — and it be told thee, and thou hear it, in whatever city you may be, you are to investigate the matter diligently and if you discover that the charge is true, you shall bring them forth to that city wherein they worshipped, and stone them.” He states that such abomination was done in Israel [implying that it is done within the nation rather than within the Land] in order to hold the worshipper [of the idols] culpable even outside the Land, for in the case of the apostate city he said, that such abomination is done ‘in thy midst,’ [within the Land], but here he mentioned within any of thy gates [a term generally limited to the Land] for it refers to common events as we have explained, and then he states in Israel in order to teach that it is binding upon the entire [nation of] Israel [even outside the Land]. It was also necessary to state within any of thy gates in order to teach that the worshipper be stoned at the gates [of the city] in which he worshipped the idols. This is [the law] in the Land, for outside the Land he is stoned at the entrance of the court where he was judged.
Now, this commandment is explanatory, since He already stated He that sacrificeth unto the gods shall be utterly destroyed, this applying in every place and at every time. Therefore he repeated it in order to explain what must be added to the commandment, but he abbreviated regarding matters previously mentioned.
And by way of the Truth, [the mystic teachings of the Cabala], it is possible that he mentioned within any of thy gates because he stated in transgressing His covenant, this [transgression] being the abomination done in [the Land of] Israel. Scripture made it known that the covenant is in the Land of the covenant, whereas he who lives outside the Land is as if he worshipped idols. I have already mentioned this subject.
He mentioned man or woman, because, due to a woman’s frivolity, she can be enticed into idol-worship through a sign or wonder done before her, the proof being the case of the women before Jeremiah. Similarly, with reference to [the witchcraft of] the ov (ghost) or yide’oni (familiar spirit), Scripture mentioned or a woman because these forms of sorcery were customarily practiced by women, as He said, Thou shalt not suffer a sorceress to live [even though both male and female sorcerers are equally liable]. And in the Sifre 148. the Rabbis interpret that [the reason for the expression or a woman is] because, having said in the case of an inciter Certain base ‘men’ are gone out from the midst of thee, implying that this law [of the apostate city] is not the same for [the inciters if they were] women, 93. it was necessary to explain that regarding an idol-worshipper the law is the same for man and woman.
The meaning of the expression which I have commanded not is already explained.

כי ימצא בקרבך, after Moses instructed the people to appoint judges in each city so that each court would judge primarily people who lived in its vicinity, Moses continues with the trial of an idolater, something that is not judged locally, in the town where he lives, but in the town in which he committed the crime. Subsequently, Moses deals with the problem of disagreements among members of the court, or several courts with one another. Such disagreements are also not to be judged locally but “in the place that the Lord has chosen,” (verse 8) i.e. the same court in which an elder who refuses to submit to the majority view of his colleagues is to be judged.

לעבור בריתו, the covenant embracing all the commandments, for worshipping idols is an offence considered as equivalent to having violated all of the Torah’s commandments.