The story
From the Bible, Paul's first letter to the Corinthians: "We shall all be changed, in a moment, in the twinkling of an eye, at the last trump" (1 Corinthians 15:52, KJV), referring to the last of seven trumpets to be sounded at the Last Judgement. The term used for the instrument in the original Koine Greek is σάλπιγξ (sálpinx), often translated as “war-trumpet”, but not resembling the modern instrument (see Seven trumpets on Wikipedia).
Etymology from Wiktionary, CC BY-SA 4.0.