The Torah states: “Lo Titgodedu1” which means “do not form separate factions”. (Gemara Yevamot 13b)
Rashi explains that if various interpretations of Halachah were to be practiced in the same place, it would seem as if the Jewish People had received two different Torahs. Alternatively, Rambam2 maintains that it would lead to arguments.
The Netziv3 was asked what Nusach (liturgy) should be prayed by an Ashkenazi davening in a Sefardi shul. All the Nuscha’ot of the different communities fulfil the basic requirements of the Gemara. The minor differences in the wording and order of davening are dictated only by custom. The Netziv ruled like the Rambam that Lo Titgodedu applies even to customs. Therefore, when davening quietly, an individual can follow his own custom; but when davening aloud, he must follow the custom of that shul.
Someone once approached the Chafetz Chaim and was bothered about the many different variations of prayer that are found within the Jewish community. Chassidim pray with their text, while Mitnagdim pray using their version of the liturgy. Even among the Chassidim there are various customs and manners how the prayer is conducted. Some daven with silent devotion, and some with great intensity and fervour. There are those who always accompany their service with tunes, and still others with dancing. Would it not be better, he asked the Chafetz Chaim, if there would be a uniform manner by which the Jews would speak to God?
“We could ask a similar question about the Russian Czar and his army,” began the Chafetz Chaim. “Why does he have so many different soldiers and ranks in his military? Some are infantry, others are cavalry, while still others are assigned to the cannon corps. Would it not be more fair and easier to administer warriors if all had the same jobs? It would seem that this would settle many problems that are necessarily a result of having so many different battalions. Yet, we all realize that each branch of the armed forces has a specific role to play. Although their overall objective is to win the battle and the war, nevertheless, the many details required to succeed demand various legions. The infantry can strike with swiftness and detail. The cavalry can overpower, while the cannons can bombard from far away. Even the bugle corps serves a purpose in that they can inspire the troops while frightening the enemy. It is only with a coordinated effort of all the soldiers that the victory can be achieved.
“Our efforts every day constitute a constant battle against the Yetzer Hara (Evil Inclination). We must always be alert to find ways to trick the Yetzer Hara and to overcome it. We need to have several types of spiritual forces to coordinate, and each must contribute its particular and unique power in defeating this enemy. One group helps to achieve victory by means of its outstanding Torah study. Another possesses the power of prayer, while yet another has the skills of singing and being joyful in the service and in whatever they do. The main thing is that everyone should do his job to the best of his ability, and that everyone realize that the victory of the nation is only due to a national effort where everyone works for the sake of Heaven.”4
1. Devarim 14:1
2. Mishneh Torah, Hilchot Avodah Zarah 12:14
3. Rabbi Naftali Zvi Yehudah Berlin, 19th century
4. Based on the article “Gemara Gem” in the Daf Yomi Digest Yevamot 14 from the Chicago Centre for Torah & Chesed