The Last Trump
"We cannot go to the Book of Revelation and say that the voice of the seventh angel (Revelation 11:15) is the last trump. In the first century, the last trump (shofar) meant a specific day in the year. In Judaism, there are three trumpets (shofarim) that have a name. They are the first trump, the last trump, and the great trump. Each one of these trumpets indicates a specific day in the Jewish year. The first trump is blown on the Feast of Shavuot (Pentecost) (Exodus [Shemot] 19:19). It proclaimed that G-d had betrothed Himself to Israel. The last trump is synonymous with Rosh HaShanah, according to Theodore Gaster in his book, Festivals of the Jewish Year, in his chapter on Rosh HaShanah. Herman Kieval also states the same thing in his book, The High Holy Days (Volume I, Rosh HaShanah, Chapter 5, Footnote 11), in the chapter on the shofar. The great trumpet is blown on Yom Kippur, which will herald the return of the Messiah Yeshua back to earth (Matthew [Mattityahu] 24:31)."
(Hebraic Heritage Ministries, http://www.geocities.com/Heartland/2175/)
(Lev 23:24 KJV) 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.
(Num 29:1 KJV) And in the seventh month, on the first day of the month, ye shall have an holy convocation; ye shall do no servile work: it is a day of blowing the trumpets unto you.
According to Num 10:10, Israel was to blow a trumpet at the beginning of each month. Since the Mosaic festival year was seven months long, the seventh month (Tishri) was the last month for a festival trumpet. This day, the first day of Tishri, which was the start of the Jewish civil year, was known as Rosh haShanah (the Feast of Trumpets or the Day of Trumpets). "The last month in the seven months' series was always sounded on this New Moon Day. This made it the final trumpets' day." (Ernest L. Martin, The Star that Astonished the World, (c)1996, pg 95)
Martin further signifies this day by relying on the work of Theodor Gaster and his book titled "Festivals of the Jewish Year." It is stated that early Jews recognized the Day of Trumpets as a type of memorial day. More than our modern versions of the holiday, it was instead a day that was symbolic of the time "when the dead return to rejoin their descendants at the beginning of the year." Martin also quotes Gaster in saying that this was "the time that became a symbol of the Last Trump." (Martin, pg 96)
(1 Cor 15:52 KJV) 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.
(1 Th 4:16 KJV) 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:
It is quite possible that Paul, being Jewish himself and surely knowledgeable of the Jewish feasts and customs, was making a symbolic reference to this time of year -- the Day of Trumpets. "The 'Last Trump' of the early Jews was when the dead were remembered. And to Paul the 'Last Trump' was the time for Jesus' second advent and the resurrection of the dead." (Martin, pg 96).