"He who curses his father and his mother, his lamp will be extinguished in deep darkness" (Proverbs 20:20). Rabbi Yudah bar Rabbi Nachman and Rabbi Levi: one of them said, this is like one who bought himself a knife in order to cut meat with it. It fell upon his finger and cut it. He said: I bought it only in order to cut meat with it; was it perhaps in order to be cut by it? So too, a person begets only for his own honor, yet they curse him. This is what is written: "He who curses his father and his mother, etc." And the other one said, this is like one who lit himself a lamp in order to enjoy its light. It fell upon his garment and burned it. He said: I lit it only in order to enjoy its light; was it perhaps in order to be burned by it? So too, a person begets children only for his own honor, yet they curse him. This is what is written: "He who curses his father and his mother."
Why a Father Who Is Cursed Loses His Lamp
Midrash Shmuel 7:1
מקלל אביו ואמו ידעך נרו באישון חשך (משלי כ' כ'), [ר'] יודה בר רבי נחמן ורבי לוי, חד מנהון אמר לאחד שקנה לו סכין להיות מחתך בה בשר, נפלה על אצבעו וחתכה, אמר לא קניתי אותה אלא להיות מחתך בה בשר, שמא להחתך בה, כך אין אדם מוליד אלא לכבודו והן מקללין אותו, הה"ד מקלל אביו ואמו וגו'. ואחרינא אמר לאחד שהדליק לו את הנר להיות נאות לאורו, נפל על בגדו ושרפו, אמר לא הדלקתי אותו אלא להיות נאות לאורו, שמא להשרף בו, כך אין אדם מוליד בנים אלא לכבודו והן מקללין אותו, [הדא הוא דכתיב] מקלל אביו ואמו.