רבינו בחיי — איש כי ידור נדר

Q — Why is the word for a vow specifically נדר? And why is the same word also used for "removing" (נדר from נדנד or מוסר)?

A — Rabbeinu Bachya — al derech haKabbalah — unfolds the double-meaning. נדר is rooted in דירה, *dwelling*: the noder is staking a claim about where his neshamah will return. Hashem is "דירתו של עולם" — the dwelling-place of the world; one who fulfills his neder demonstrates faith that his soul will eventually be re-housed there. So the act of vowing *is* the act of dwelling-in-advance. But vowing has an inverse mode: one who breaks his vow has removed himself from that very dwelling — and the word נדר, in its other valence, is precisely the language of removal ("מוסר מאותה דירה"). The Hebrew root contains both gestures, like the Latin sacer that means both holy and accursed. The choice the noder makes is therefore not a small matter of speech-ethics but a cosmological vote about where his neshamah is heading. ככל היוצא מפיו יעשה is, in this reading, a clause about residency.