Sifrei Bamidbar 14

(Bamidbar 5:21) "Then the Cohein shall beswear the woman with the oath of the curse." What is the intent of this? Because it is written (Vayikra 5:1) "and he hear the voice of a curse," this tells me only of a curse. Whence do I derive that an oath is like a curse? It is derived inductively, viz.: It is written here (Bamidbar) "curse," and it is written elsewhere (Vayikra) "curse." Just as here "oath" is equated with "curse," (viz. "the oath of the curse"), so, there, "oath" is equated with "curse." And just as here, (the oath is administered) with "yod-keh" (viz. Ibid. "May the L-rd [yod-keh-vav-keh] render you, etc."), so, all the oaths in the Torah (are administered with) "yod-keh." "in the midst of your people": and your people (will remain at) peace. "in the midst of your people": and not at this time (when you are in the midst of gentiles.) There is a (crucial) difference between one being degraded in a place where he is known, and one being degraded in a place where he is not known, (the former degradation being more severe).