The Torah uses the Hebrew word "bagdah" in connection with a father who has sold his daughter as a maid-servant (Exodus 21:8). The Mekhilta interprets this word as a description of the father's betrayal. By selling her, he degraded her. He did not treat her as a Jewish daughter deserves to be treated. He was faithless to her.
Rabbi Yonathan ben Avtalmos draws a significant legal consequence from this characterization. Because the father has already been faithless to his daughter once by selling her, he is not permitted to retain the power to sell her again. His act of betrayal, the initial sale, exhausts his authority. The word "bagdah" is not merely descriptive. It is the legal basis for the prohibition against selling a daughter into servitude a second time.
The Mekhilta then demonstrates that "bagdah" consistently carries the meaning of deceit and faithlessness throughout Scripture. The prophet Malachi uses the same word: "Yehudah has dealt faithlessly (bagdah)" (Malachi 2:11). Jeremiah employs it as well: "For the house of Israel has dealt very treacherously (bagod bagdu) against Me" (Jeremiah 5:11). In both prophetic contexts, the word describes a profound violation of trust, a betrayal of a relationship that should have been sacred.
By connecting the father's sale of his daughter to the same vocabulary the prophets use for national betrayal of God, the Mekhilta elevates the seriousness of the act. Selling a daughter is not a neutral commercial transaction. It is an act of faithlessness that the Torah names with the same word reserved for the worst forms of covenantal betrayal. The language itself imposes the punishment: one betrayal is all you get. There will not be a second.