Commentary for Leviticus 20:9

אביו ואמו קלל HE HATH CURSED HIS FATHER OR HIS MOTHER — These apparently redundant words are intended to include as subject to the death penalty one who curses his parents after their death (Sanhedrin 85b).

FOR WHATSOEVER MAN THERE BE THAT CURSETH HIS FATHER OR HIS MOTHER. The meaning thereof is that it refers back to the beginning of the section where He stated, Ye shall fear every man his mother, and his father,²³³Above, 19:3. and He now states here, for whatsoever man there be that does not obey [this commandment] and curseth his father, or his mother, he shall surely be put to death, and by way of the Truth, [the mystic teachings of the Cabala], this verse is here stated because He had said [above], Sanctify yourselves therefore, and by ye holy; for I am the Eternal your G-d,²³⁴Verse 7. and I am the Eternal Who sanctify you,²³⁵Verse 8. meaning that it is the Glorious Name²³⁶Deuteronomy 28:58. Who sanctifies us, for He is our Father, and our Redeemer from everlasting,²³⁷Isaiah 63:16. and it is His Name; therefore he who curses those who participated in his formation, is liable to death. This is the reason for the law [of the punishment] of the adulterer and adulteress, [in the following verse], which He placed near here before [the law of] all forbidden relations [mentioned further on in this section].²³⁸Ramban’s meaning, as clearly indicated by his commentary (see following note) is that as a result of committing adultery the children of the union may come to transgress the laws relating to parental honor, as they will not know who their fathers are. It is for this reason that the law of the adulterer and adulteress is identical to that of one who curses his parents [who is liable to death by the hand of the court], as the one leads to the other, and therefore too, it is mentioned in juxtaposition to that law. I have already alluded to this above.²³⁹Exodus 20:13 (Vol. II, p. 320).
Now Scripture mentions here some of the forbidden relations in order to make [one who has intercourse with them] liable to death, these being a man’s wife,²⁴⁰Verse 10. a father’s wife,²⁴¹Verse 11. a daughter-in-law,²⁴²Verse 12. a male,²⁴³Verse 13. a woman and her mother,²⁴⁴Verse 14. and the same law applies to a woman and her daughter and her daughter’s daughter, for He mentioned here only some of the relations of a wife, but the same punishment applies to all those mentioned there²⁴⁵Above, 18:17. in the admonition. And surely this applies all the more so to one’s own relatives, such as his son’s daughter and his daughter’s daughter mentioned there,²⁴⁶Ibid., Verse 10. and needless to say, his [own] daughter. On all these matters there are also Rabbinical interpretations to establish their punishment. Similarly He mentioned here the punishment of death for lying with a beast.²⁴⁷Verse 15. He mentioned excision again in the case of a menstruant²⁴⁸Verse 18. [although this has already been included in a general statement above, 18:29], in order to declare him liable for mere sexual contact without completion of the act, this being the sense of the expression, he hath bared her fountain.²⁴⁸Verse 18. Similarly [He has stated] in the case of a mother’s sister and a father’s sister, for he hath bared his near kin.²⁴⁹Verse 19. He mentioned an uncle’s wife²⁵⁰Verse 20. and also a brother’s wife,²⁵¹Verse 21. in order to declare them liable to [the punishment of] dying childless, whether he had no children at the time when he commits the sin, or he did have [in which case none will survive him]. But the excision mentioned in the case of one’s sister²⁵²Verse 17. is redundant [being included in the general statement above, 18:29], and has therefore been interpreted by our Rabbis:²⁵³Makkoth 13 b. “Why was excision specified in the case of a sister etc.” In line with the plain meaning of Scripture [excision was specified in the case of a sister] in order that Scripture should add [that it will be done] in the sight of the children of their people,²⁵²Verse 17. meaning to state that their soul will perish in youth²⁵⁴Job 36:14. in such a way that people will see, understand and realize that the hand of the Eternal hath done this,²⁵⁵Isaiah 41:20. and that the Holy One of Israel has decreed it.
The meaning of the expression he shall bear his iniquity,²⁵²Verse 17. is that this sin will cleave to him from that time onwards, his deeds will not prosper, and the curse shall lie upon him,²⁵⁶See Deuteronomy 29:19. for G-d will strike him with sore sicknesses until He will destroy him with excision, something similar to what the Rabbis have said:²⁵⁷Shabbath 37 a. “A sign of [this type of] sin is one affected with dropsy.” It was not necessary for Scripture to mention the other people who are liable to excision, such as one’s mother²⁵⁸Above, 18:7. and a wife’s sister,²⁵⁹Ibid., Verse 18. because all that is needed to be stated about them we have already derived from those mentioned [here in this section].

כי איש איש אשר יקלל, proof that I, G’d, am so insistent that your sanctity be manifest by your seed being genealogically pure is that the penalty for non observance is the execution of the person who curses his parents. The normal scenario which leads to a son or daughter cursing their parents has to do with legitimacy or otherwise of their offspring. When a son or daughter are the product of unions forbidden under the laws of incest, children of such unions have little reason to practice the commandment to honour their parents as it was from their parents that they learned to ignore Torah legislation. Solomon’s well known instruction שמע בני מוסר אביך ואל תטוש תורת אמך, “heed the moral instruction of your father, and do not ignore the teachings of your mother” (Proverbs 1,8) are most difficult to honour when they know they have seen the light of day only because their parents chose to ignore this very instruction.