"And in the seventh month, on the first of the month, you shall have a holy celebration — it shall be a day of blowing the shofar for you" (Numbers 29).

The Jewish New Year is characterized by one of the most mysterious mitzvot in the entire Torah — blowing the shofar. Every other major Jewish holiday finds us performing certain acts, such as learning Torah all night on Shavuot, or saying special prayers, such as the confession of sins on Yom Kippur.

But Rosh Hashanah, the first day of the Jewish year and the birthday of the world's creation, commands none of these.

It almost seems that when Rosh Hashanah's turn came around for mitzvot, God teased the people by giving them a mitzvah they could fulfill only through their sense of hearing.

The shofar is one of the earliest musical instruments known to humans. It is made from the horn of a kosher animal — except for cows, which apparently lost out on the "privilege" following the infamous Golden Calf escapade.

Shofars tend to come from the horns of the animal most prevalent in the countries where Jews lived. In Ashkenazi Europe, for example, they were usually made from ram horns, whereas in Ethiopia they were made from the horns of African antelopes known as kudus.

The size of a shofar doesn't matter, as long as it is longer than the width of a person's hand. The largest spiraling kudu horns stretch the length of an arm.

Each shofar has its own distinctive sound. According to professional musician and shofar-blowing instructor David Lloyd Perkins, the longer the shofar, the easier it is to play and produce harmonics.

"On a short ram's horn I can get three harmonic tones," says Perkins, "but on a long kudu shofar I can produce between nine and 12 harmonics."

Perkins has blown his shofar in such diverse locales as the roof of the Vatican, and in Seoul, Korea, on Israel Independence Day 1995 when he served as an official representative of the Israeli government.

Playing the shofar is not difficult, Perkins asserts.

"Even the 3- and 4-year-olds in my classes play the shofar wonderfully," he says. Sometimes, however, "the mouthpiece cut into the shofar is too small, which is very often the case with the factory-produced shofars."

What should the correct mouthpiece size be?

"Big enough to be comfortable for human lips," says Perkins, who heats the ends of his shofars in order to enlarge the mouthpieces.

Harmonics, note range, and tone are very important when the Rosh Hashanah shofar sounds are taken into consideration.

There are four distinct shofar sounds for the Rosh Hashanah service. The tekiah is one long blast with a clear tone. The broken shevarim is a sighing sound of three short calls. The teruah is an alarm, a rapid series of nine or more very short notes. And tekiah gedolah is the great, unbroken blast held as long as possible.

In fact, no one really knows what the blast should sound like. It could be a shevarim, a teruah or a combination of both. On Rosh Hashanah, several combinations are used to accommodate the various rabbinic opinions.

To add to the irony of the shofar-blowing mitzvah, the command is given in the Torah without explanation. However, Torah sages throughout history have offered numerous reasons for why Jews must blow the shofar and hear the shofar.

Maimonides, the medieval Jewish philosopher and physician, likens the reason to a wake-up call to all Jews.

In his Laws of Repentance, Maimonides writes: "Awake, sleepers from your sleep! Arise, slumberers from your slumber! Scrutinize your deeds, return to repentance and remember your Creator. Those forgetters of the truth in the vanities of time and those who stray all their year in vanity and emptiness which can neither help nor save, look into your souls, better your ways and deeds! Let each of you abandon your evil way and your thoughts which are not good."

The famous List of 10 Symbolic Meanings of Rav Sa'adia Gaon (Rabbi Sa'adia the Genius) is still studied today, more than 1,000 years after it was published in the early 900s.

He wrote that the sounds remind us of the words of the prophets, which in the Book of Ezekiel (Chapter 33) were compared to the sounding of a shofar. "And whoever hears the sound of the shofar and takes no warning — if the sword comes and takes him away, his blood shall be on his own head; because if he had taken warning, he would have saved his soul."

The blasts, the rabbi wrote, also remind us that Yom Kippur is just around the corner. It's time to get down to the eternally important business of repentance.

The shofar, with its otherworldly and piercing calls, can help unlock our hearts at the annual moments of utmost importance. In the end, perhaps the mitzvah of blowing the shofar isn't as mysterious as we thought.