Feast of Blowing the Trumpets/ Yom Teruah

The Shofar which is made from a Ram's Horn, was used on the seventh day after the seven priest went around the city of Jericho seven times Joshua 6:4-5

The prophets linked the blowing of trumpets to the future Day of Judgment:
Joel 2:1
Zephaniah 1:14 -16

YHWH instructed that only the sons of Aaron, the Levitical Priesthood, had the authority to blow these trumpets, Numbers 10:8.

The Feast of Blowing the Trumpets/ Yom Teruah, literally means to make a loud noise. This word can describe the noise made by a trumpet but it also describes the noise made by a large gathering of people.  This is a day appointed by YHWH in the seventh month on the first day of the month occurring in the fall (Leviticus 23:24 -25; 1 Kings 8:2).  This month stands out as a month that brings in the last three annual feasts, namely, Trumpets, Atonement and Tabernacles.  The number seven represents completion and termination, this gives us the understanding that these three feasts of the seventh month, completed the yearly cycle of sacrifices and harvest.  This day is a memorial which marks the beginning of "Ten Days of Repentance," these are the ten days of preparation for the Day of Atonement (Yom Kippur), which falls on the tenth day of the seventh month. The Israelites were commanded to keep it as a Sabbath day/Day of rest.  No occupational work shall be done on this day and you were to have a holy convocation, a large assembling of people Numbers 29:1. You can cook on this day because it is a feast day.

History of Trumpets

In the Hebrew culture trumpets play a significant role and were commanded to be used.  The Creator commanded that Israel use two types of trumpets. 

Two silver trumpets were used for Numbers 10:1-10:

the calling of the assembly
for the journeying of the camps
to sound an alarm 
In the days of our gladness
In our solemn days (feast days)
In the beginning of the months
To gather the rulers whom judged the people Exo.18:13-27
To gather the congregation together
When going to war