Keep Your Word

The possuk at the end of the parsha of nedarim sums up the laws: אֵ֣לֶּה הַֽחֻקִּ֗ים אֲשֶׁ֨ר צִוָּ֤ה י״י֙ אֶת־מֹשֶׁ֔ה בֵּ֥ין אִ֖ישׁ לְאִשְׁתּ֑וֹ בֵּֽין־אָ֣ב לְבִתּ֔וֹ בִּנְעֻרֶ֖יהָ בֵּ֥ית אָבִֽיהָ.  However, what is ignored is the basic law itself that one must keep their neder.  Why? 

The Mishne L’melech Melachim (10:7) brings a machlokes in the Yerushalmi Nazir (9:1) if a gentile is obligated in בל יחל דברו.  The Mishne L’melech asks that we find many times that gentiles have to keep their word?  The Avnei Nezer Yorah Deah (306) explains that it is a סברא that one must keep their word and that is incumbent upon gentiles as well.

Based upon this we understand that the chiddush of the Torah is the din that a neder can be canceled; the need to fulfill one’s neder is self-understood (see Likutay Sichos volume 13.)