Kommentar zu Dewarim 27:16

מקלה means, “making light of”, it has the same meaning as (Deuteronomy 25:3) “Lest … thy brother become despicable (נקלה).

ארור מקלה אביו ואמו, "Accursed is anyone who degrades his father or his mother." It is important to examine why Moses selected that only people guilty of non-observance of these eleven out of a total of 613 commandments were deserving to be publicly declared as being accursed? Are there not some more severe violations, such as the violation of commandments dealing with incest which would qualify no less for the treatment we see here accorded to the violators of these eleven commandments? Is it not difficult to consider adultery as less serious than moving a boundary stone, for instance?

Perhaps the Torah here enumerates only sins which are normally committed in secret, or which will not be revealed by their victims. This may be the reason why the Torah speaks of ושם בסתר, "and emplace it in secret" (verse 15 where the sin is idolatry). If that sin would be committed in public the sinner would not merely be accursed but he would be executed and the Israelites themselves would be charged with seeing to it that he does not get away with his sin. The same consideration may apply to someone who degrades his father or mother. The Torah speaks of people who do this in private where the hand of the law cannot reach them. This is why Moses wants to make it plain that they will be accursed by the heavenly tribunal. The same consideration applies to someone who moves boundary stones or fences in a manner which is hard to detect. Not only that, who can prove who has moved the boundary? How are we going to convict the culprit? Similarly, the son-in-law who sleeps with his (consenting) mother-in-law is untouchable by the terrestrial courts so that the Torah has to demonstrate by this means that such people are not immune to the consequences of their actions. The reference to someone who strikes his fellow in secret, i.e. where there are no witnesses, is another such example of offences which cannot be adjudged by a terrestrial court seeing that the evildoer will deny having hit the other fellow, or he may not even be accused of doing so if he acted under cover of darkness or wore a mask, for instance.

The reason the Torah inserted the offence of sleeping with a beast between the sin of sleeping with the wife of his father or the sin of sleeping with his sister, is to suggest that commission of either sin is as unlikely as having sexual intercourse with an animal. All three sins represent the most abominable aberration of which one can become guilty.