Following the exile from the Land of Israel, and the scattering of Jewish communities, distinctions were created among the diverse ethnic groups (eidot) regarding the wording of the prayers. In the main prayers, those instituted by Anshei Knesset HaGedolah, such as Birkot Keriat Shema and the Amidah, the differences are very slight. Even in the main passages of the Korbanot (sacrificial offerings) and Pesukei d’Zimrah, which were established during the time of the Talmud and the Geonim, the disparities are minor. The modifications are more noticeable, however, in the supplements added during the period of the Rishonim, such as additions to the Korbanot passages and prayers concluding the service. What was customary to include in Spain was not necessarily accepted in Ashkenaz, and vice versa. This is especially apparent in the liturgy for the High Holy Days and Festivals, composed during the time of the Geonim and Rishonim. Hence, we find completely different piyutim (poems) in the High Holy Day prayers of the Sephardic and Ashkenazic services.
It is proper that every Jew continue in his family’s custom. Even if he knows that a certain nusach is more precise, the continuation of tradition is more important than the accuracy of one word or another.
The Ari HaKadosh clarifies the differences in wording and style between Sephardim and Ashkenazim. He explains that there are twelve windows in the heavens corresponding to the twelve tribes of Israel and the prayer of each tribe ascends through its particular gate. That is the enigma of the twelve gates mentioned at the conclusion of the book of Ezekiel (Sha’ar HaKavanot p. 50, 4; Magen Avraham 68:1; Mishnah Berurah 68:4).
Additionally, distinctions exist among the ethnic groups regarding the pronunciation of certain Hebrew letters, e.g., tzadi and kuf, as well as vowels, such as, kamatz and cholam and each group must continue its custom. If, however, people change their nusach, they still fulfill their obligation, for all the existing Jewish traditions relating to the reading of letters and vowels are permitted for prayer (Igrot Moshe Orach Chaim, part 3, 5; additionally, even regarding the wording of the Chalitzah ceremony in which, according to all opinions, every letter must be enunciated, one may fulfill his obligation in any ethnic accent).