The last trump essentially marks the change between the rule of men, and the rule of Yeshua on Earth. The beginning of the 1000 year reign.
It is spelled out twice in Revelation.
Revelation 20:
[4] And I saw thrones, and they sat upon them, and judgment was given unto them: and I saw the souls of them that were beheaded for the witness of Jesus, and for the word of God, and which had not worshipped the beast, neither his image, neither had received his mark upon their foreheads, or in their hands; and they lived and reigned with Christ a thousand years.
[5] But the rest of the dead lived not again until the thousand years were finished. This (those that lived and reigned with Christ for a thousand years) is the first resurrection.
[6] Blessed and holy is he that hath part in the first resurrection: on such the second death hath no power, but they shall be priests of God and of Christ, and shall reign with him a thousand years.