A shofar is an instrument made from the horn of a ram or other kosher animal. It was used in ancient Israel to announce the New Moon (Rosh Chodesh) and call people together. It was also blown on Rosh Hashanah, marking the beginning of the New Year, signifying both need to wake up to the call to repentance, and in connection with the portion read on the second day of Rosh Hashanah, the Binding of Isaac (Genesis, chapter 22) in which Abraham sacrifices a ram in place of his son, Isaac.
Today, the shofar is featured most prominently in the Rosh Hashanah morning services. It is considered a commandment to hear the shofar blown.
There is a great deal of symbolism tied in with the legal requirements for what constitutes a proper shofar. The shofar of Rosh Hashanah, whose purpose it is to rouse the Divine in the listener, may not be constructed of an artificial instrument. It must be an instrument in its natural form and naturally hollow, through whom sound is produced by human breath, which God breathes into human beings. This pure, and natural sound, symbolizes the lives it calls Jews to lead. What is more, the most desirable shofar is the bent horn of a ram. The ram reminds one of Abraham's willing sacrifice of that which was most precious to him. The curve in the horn mirrors the contrition of the one who repents.
In the Talmud, we read: Rabbi Abbahu said:
According to Leo Rosten, “The bend in the shofar is supposed to represent how a human heart, in true repentance, bends before the Lord. The ram's horn serves to remind the pious how Abraham, offering his son Isaac in sacrifice, was reprieved when God decided that Abraham could sacrifice a ram instead. The man who blows the shofar is required to be of blameless character and conspicuous devotion; he must blow blasts of different timbre, some deep, some high, some quavering.”