(Devarim, Ibid. 19) "Peoples at the mountain will assemble": Where is it seen peoples and rulers would explore the commerce of Eretz Yisrael and say: Since we have troubled ourselves to come here, let us look into the business of the Jews, and they would go up to Jerusalem and see (all of) Israel serving one G-d and eating one (kind of) food (— for with the Babylonians, the god of one was not like the god of the other, nor the food of one like the food of the other —), and they would say: It is only to such a nation that it is fitting to cling — Whence is it seen that they did not depart from there until they had converted (to Judaism) and offered up sacrifices and burnt-offerings? From (Devarim, Ibid.) "There they will sacrifice sacrifices of righteousness."
Foreign Traders Who Converted After Visiting the Mountain
Sifrei Devarim 354:5