In the Torah, (the Five Books of Moses) the Hebrews are given a commandment that on the first day of the seventh month (Tishrei) of the Hebrew calendar “you shall observe complete rest, a sacred occasion commemorated with loud blasts.” (Leviticus 23:24) These loud blasts, or teruah, were understood by the rabbis to allude to the blasts of the shofar. So on Rosh Hashanah (the Jewish New Year which this year falls on 26th September), we blow the shofar in order to fulfill this commandment. The biblical text doesn’t go into precisely the reason that it’s so important that we hear a teruah, (shofar musical note) but there are a few possibilities.
You might imagine that a shofar was chosen for Rosh Hashanah just because it was the only horn-like instrument that the Israelites had in the desert when they were given the commandments. But actually, the Torah mentions a number of instruments the people had with them, including silver trumpets, so the use of the shofar doesn’t seem to have been borne from necessity.
The Bible contains many explicit references to the shofar, not just the Rosh Hashanah commandment. When the people receive the 10 Commandments from God on Mount Sinai, they hear a very loud blast of the shofar. We’re commanded to blow the shofar not only on Rosh Hashanah, but also at the beginning of the Jubilee year. Shofars were also blown by warriors in battle, and by musicians in the temple.
The sound of the teruah is both earthly and divine. It comes from an animal, but makes the same sound that was heard on the top of Mount Sinai when God addressed the people. Music can be celebratory, but the sound of the shofar is more than just a sound of jubilation. It is the sound of the presence of God, and the sound we use to cry out to God when we need God’s intervention.
The Torah struggles with the same question that we have. In Tractate Rosh Hashanah 16a we read: “R. Abbahu said: Why do we blow a ram’s horn? The Holy One, blessed be He said: Sound before Me a ram’s horn so that I will remember on your behalf the binding of Isaac, the son of Abraham, and to account it to you as if you had bound yourselves before me.”
In this case, Rabbi Abbahu is claiming that the shofar is an allusion to the ram we read about in the story of the binding of Isaac, which is the Torah reading for Rosh Hashanah. The shofar reminds us of the sacrifice Abraham made, and we use it to remind God of that same sacrifice, so that He’ll credit their good actions to us, today. (Remember, in the end of that story, Abraham sees a ram and sacrifices it instead of Isaac.)
In your question you asked about why we don’t use a real trumpet, and I think it’s reasonable to consider that a trumpet is perhaps too technical for the function that a shofar serves. Trumpets have evolved over time, and there are many different kinds of horns, from bugles to cornets to French horns to sousaphones. Those instruments are all regulated to sound a certain way. But a shofar is taken from a living being. Every shofar sounds different, just like every community, and every listener, is different.
To get a little more insight on this issue, I contacted Rabbi Josh Feigelson, campus rabbi and senior director for educational initiatives at Northwestern University Hillel. Rabbi Feigelson is a trained tubist, and he wrote to me about some of the differences between playing the tuba (a brass instrument, like a trumpet) and blowing the shofar:
Pitch is not so much an issue in playing the shofar. You’re not out to create a melody, which you are trying to do when playing the tuba. When I’m playing the shofar I’m more focused simply on the sound… The shofar isn’t a musical instrument. It is a battle cry, or a mournful cry, but its symbolism comes from its sound and the fact that it is the shofar making the sound on the day of Rosh Hashanah. The tuba has no inherent symbolism, and its sounds are ultimately judged and understood within the context of a melody or a larger work.
Also, he reminded me that shofars are notoriously stinky. Other brass instruments do not tend to carry quite the same level of aroma.
I also think there’s something to be said for the primitive nature of the shofar. It is nature-made. It is simple. Many people think that a teruah sounds like a voice crying out. Isn’t it appropriate for the instrument that calls us to reflect and repent to sound like a human voice?
All that said, did you know there are some pieces of classical music that call for the use of the shofar? Edward Elgar’s oratorio The Apostles includes a shofar, and Lester Bowie, a famous jazz trumpeter, was known for sometimes playing the shofar with the Art Ensemble of Chicago!