Tafsiran Ulangan 27:19: Ibn Ezra & Chizkuni

perverts the justice of the alien or orphan Scripture mentions the alien, the orphan, and window, because these people have no allies, so to mistreat them is also an act committed in private. If a judge were to pervert the justice of others, they would appeal against him, and thus subject him to public scrutiny. But aliens, orphans and widows have no power. Someone who lies with his father’s wife (or his sister [: 22], or his mother-in-law [: 23]) typically does so in complete secrecy, because he does not fall under any suspicion for being alone with her. This is not the case with respect to the other forbidden sexual relations.

גר, יתום, ואלמנה, “a stranger, orphan, or widow;” all these categories of people lack influential friends or protectors who will protest their having been maltreated to the authorities. People who have carnal relations with their closest relatives who live in the same house with them are not suspected of having been guilty of such behaviour, neither are people normally suspected of having sexual relations with their domestic animals. The only two sins listed here which are committed openly are idolatry and violent behaviour against one’s neighbour committed usually while angry and out of control. This is why the Torah adds the word “committed secretly,” when speaking of these two sins. When these two sins are committed openly there is a court which can take action against the perpetrator.