G-d commanded the Israelites to commemorate the day with trumpet blast along with a sacrifice and a day of rest.
Leviticus 23:23-25, TLV Version
Adonai spoke to Moses saying: 24 “Speak to Bnei-Yisrael, saying: In the seventh month, on the first day of the month, you are to have a Shabbat rest, a memorial of blowing (shofarot), a holy convocation. 25 You are to do no regular work, and you are to present an offering made by fire to Adonai.”
Rosh HaShanah commemorates the creation of the world and marks the beginning of the Days of Awe, a 10-day period of introspection and repentance that culminates in the Yom Kippur holiday also known as the Day of Atonement.
Rosh HaShanah and Yom Kippur are the two “High Holy Days” in the Jewish faith.
Many believers in Yeshua look forward to His coming at the time of the blowing of the shofar, when Messiah will come like a bridegroom coming for His bride.
1 Thessalonians 4:16-17