According to the God-designed Bible Calendar (i.e. Exodus 12:2), the first day of the month of Tishri (which is the seventh month on The Lord's calendar, see Bible Months) is a Holy Day to Jews throughout Israel and the world. They call it Rosh Hashanah. To Christians, it's known as the Feast of Trumpets.
The Jewish Rosh Hashanah
Jewish tradition holds that Rosh Hashanah celebrates the anniversary of the creation of the world (see The Seven Days Of Creation), a day when "God takes stock of all of His Creation," which of course includes all of humanity. Translated from the Hebrew, Rosh Hashanah means "head of the year" - rosh means head, while hashanah means year. Jews believe that God's judgment on this day determines the course of the coming year.
Rosh Hashanah is a Jewish festival in which most work ceases, just as on the weekly Sabbath. It's celebrated both in joy and solemnity. During the daily prayer service a ram's horn, or in the Hebrew, shofar (example shown above) is sounded:
"And The Lord [see YHVH, Adonai, Jehovah, LORD] spake unto Moses [see also The Education Of Moses], saying, Speak unto the children of Israel, saying, In the seventh month, in the first day of the month, shall ye have a sabbath, a memorial of blowing of trumpets, an holy convocation. Ye shall do no servile work therein: but ye shall offer an offering made by fire unto The Lord." (Leviticus 23:23-25 KJV)
The Christian Feast of Trumpets
God does not do things in vain, or without purpose. The Old Testament (see The First Christian Bible) Holy Days were not just some sort of Divine make-work project to keep the Israelites busy while they were out wandering in the desert (see Wilderness Journey). All of the Old Testament Holy Days (Passover, Unleavened Bread, The Feast of Weeks/Pentecost, The Feast of Trumpets, The Day Of Atonement, The Feast Of Tabernacles and The Eighth Day - see also Christian Living) were, and continue to be, living symbols of the stages of God's Plan of Salvation for all humanity. Those events are now in progress, and true Christians, who are spiritual Israel (see Physical and Spiritual Israel and Daughter of Zion) are the manifestation of it.
In the Christian world, Rosh Hashanah is known as The Feast Of Trumpets. Many Christians observe this festival for its Christian prophetic application - The Return Of Jesus Christ and the first resurrection (see Resurrections). Just as Christ, the Lamb of God, was sacrificed at Passover (in spring, in the northern hemisphere), for which The Lord instituted Passover to symbolize and foreshadow, it is very likely that His return will be at the time of the Feast of Trumpets (in autumn, in the northern hemisphere), for which The Lord instituted the Feast of Trumpets to symbolize and foreshadow.
"Behold, I show you a mystery; We shall not all sleep, but we shall all be changed, In a moment, in the twinkling of an eye, at the last trump: for the trumpet shall sound, and the dead shall be raised incorruptible, and we shall be changed. For this corruptible must put on incorruption, and this mortal must put on immortality." (1 Corinthians 15:51-53 KJV) [see "That which is born of the Spirit is spirit"]"For this we say unto you by the word of the Lord, that we which are alive and remain unto the coming of the Lord shall not prevent them which are asleep. For the Lord himself shall descend from heaven with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first: Then we which are alive and remain shall be caught up together with them in the clouds, To Meet The Lord In The Air: and so shall we ever be with the Lord." (1 Thessalonians 4:15-17 KJV) (see also When Will You Be Judged?)
Fact Finder: How did Jesus Christ Himself describe His own future Return, and how will the sounding of a trumpet be involved?
Matthew 24:30-31