Amen signifies divine confirmation from truth, consequently from the Lord himself because the Lord was truth itself. Therefore he so often said, "Amen I say unto you" (Matthew 5:18, 26, Revelation 3:14).

God is called the Amen, the faithful and true witness that the Lord is the truth itself. See John 14:16, 17, 19.

In Revelation 1:7, amen signifies divine confirmation. (Apocalypse Explained 40)

In Revelation 7:12, as the Lord was Truth Itself, He often said: AMEN, or VERILY, I say unto you. (Apocalypse Revealed 375, Apocalypse Explained 23)

(References: Apocalypse Revealed 23, 292)