The shofar is mentioned frequently in the Hebrew Bible, the Talmud and rabbinic literature. The blast of a shofar emanating from the thick cloud on Mount Sinai made the Israelites tremble in awe (Exodus 19, 20).
The shofar was used in to announce holidays (Ps. lxxxi. 4), and the Jubilee year (Lev. 25. 9). The first day of the seventh month (Tishri) is termed "a memorial of blowing" (Lev. 23. 24), or "a day of blowing" (Num. xxix. 1), the shofar. It was also employed in processions (II Sam. 6. 15; I Chron. 15. 28), as a musical accompaniment (Ps. 98. 6; comp. ib. xlvii. 5) and to signify the start of a war (Josh. 6. 4; Judges 3. 27; 7. 16, 20; I Sam. 8. 3). Note that the 'trumpets' described in Numbers 10 are a different instrument, described by the Hebrew word 'trumpet' not the word for shofar.
The Torah describes the first day of the seventh month (1st of Tishri = Rosh ha-Shanah) as a zikron teruah (memorial of blowing; Lev. xxiii) and as a yom teru'ah (day of blowing; Num. 29). This was interpreted by the Jewish sages as referring to the sounding the shofar