The shofar is an ancient instrument that emits a loud, clear sound which may be heard from a great distance and it originally served to summon the army in case of emergency and to proclaim holidays and festivals. The Bible mentions the shofar more than 70 times, attesting to its significance in Jewish tradition. According to Isaiah's prophecy, at the End of Days the sound of the shofar will herald the redemption of the Jewish people and their return to the Land of Israel from the Diaspora, "And in that day, a great ram's horn shall be sounded, and the strayed who are in the land of Assyria and the expelled who are in the land of Egypt shall come" (Isaiah 27,13),
The shofar's significance is especially highlighted on the first day of Rosh Hashanah, which the Torah refers to as the "Day of Shofar Blasts". The Book of Numbers (29, 1) states that "in the seventh month, on the first day of the month... a day when the horn is sounded". This statement is somewhat surprising - why is the blowing of the shofar noted as the central commandment on Rosh Hashanah, the day when, according to Jewish belief, all people are judged before God?
The answer to this question lies in the Babylonian Talmud, Rosh Hashanah tractate page 17A, "Rabbi Abbahu said... the Holy One, blessed be He, said 'Sound before Me on a cornet made of a ram's horn, that I may remember you, for your sake, the offering of Isaac, the son of Abraham"'. The sound of the shofar, made of a ram's horn, was meant to remind those who hear it of the strength of Abraham's faith, as he was prepared to sacrifice his son and of God's mercy, as He called forth a ram for Abraham to sacrifice in place of-his son.
During the Temple period, the priests played various instruments, such as horns and shofars, while performing their holy duties. Other instruments were also noted in the Book of Psalms, psalm 150, "Praise Him with the blasts of a horn, praise Him with harp and lyre. Praise Him with timbre) and dance, praise Him with lute and pipe". After the destruction of the Temple, the custom of playing instruments during prayer ceased and only the use of the shofar remained.
The Wisemen learned from the Torah that the "teruah" blast (series of blasts) is to be blown three times, each preceded and followed by the "teki'ah" (long single blast). Since they were unclear as to precisely what kind of blast was referred to in the Torah, whether "shvarim" (three short blasts) or "teruah" (series of nine staccato blasts) or a combination of the two, it was decided that all three would be heard during prayer. The three combinations of the shofar blasts appear on the stamp tabs. The First Day Cover features the text of the blessing recited in the synagogue prior to blowing the shofar.
The shofars used by Jews of varying origins are mostly made of ram's horn, while the Jews of Yemen use a twisted shofar made from the horn of an African antelope, called a Kodu.