Answer : Yom Teruah — The Feast of Trumpets
The feast in question is Yom Teruah, the Feast of Trumpets, more commonly known in rabbinic Judaism as Rosh Hashanah, the Jewish New Year.
The main scriptural references are Leviticus 23:23–25 and Numbers 29:1–6, the latter focusing mainly on the offerings prescribed for that day.
In Leviticus, it is called “a holy convocation” and “a memorial of blowing of trumpets” (yom hazikaron teruah). Yet the text does not specify what is to be remembered or why the trumpets are to be blown. The reason for this convocation is left unstated, creating an intriguing mystery that later Jewish commentators also noticed.
Medieval rabbis such as Ibn Ezra (12th century) referred to this as a religious mystery, while Abarbanel (15th century) wondered why the Torah gives no clear explanation for the feast’s purpose.
However, the meaning emerges when Yom Teruah is viewed within the prophetic sequence of Israel’s seven feasts. It is the fifth feast, the first of the fall festivals, and it prophetically points to the Rapture of believers.
In the Brit Chadashah (New Testament), particularly in 1 Corinthians 15:51–57 and 1Thessalonians 4:13–18, the mystery is unveiled: “At the last trumpet, the dead will be raised incorruptible, and we shall be changed.”
At the sounding of the trumpet, there will be a holy convocation of all believers—those who have fallen asleep and those who are alive—caught up to meet the Lord in the air. Thus, what was once an unexplained memorial in the Torah becomes, in the light of Messiah, a prophetic picture of the great gathering of the redeemed.