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)

23. From Him who is, and who was, and who is to come, signifies from Him who is the All in all things of heaven and of the church from eternity to eternity. This is evident from the signification of "who is, and who was, and who is to come," as being from eternity to eternity, also the All in all things of heaven and of the church. From eternity to eternity is meant, because all times in the Word signify not times but states of life (as may be seen from what is said and shown concerning Time in Heaven, in the work on Heaven and Hell 162-169; and as all times signify states of life, so in reference to the Lord they signify infinite state, and infinite state as to time is eternity. That all times are comprised in "who is, and who was, and who is to come," is evident. Of eternity, which is of the Lord alone, many things might be said; but such things are not understood by the natural man, whose thoughts are chiefly based on time, space, and matter, while, nevertheless, eternity, in itself, does not include such things.

If, indeed, man could think of eternity as the angels of heaven do, he might arrive at some idea of it, and thus might comprehend what from eternity is, which is signified by "who was;" also what the Divine foresight is, that it is in the most particular things from eternity; and what Divine Providence is, that it is in the most particular things to eternity; consequently, that whatsoever proceeds from the Lord is from eternity to eternity; and unless it were so heaven and the universe would not subsist. But there is no time to go further into this arcanum as yet something may be seen respecting it in the work on Heaven and Hell 167; only let it be known, that the like is meant by "Jehovah" as by "who is, who was, and who is to come," since "Is," which is the meaning of Jehovah, involves what precedes, that is, "who was," and also what is future, that is, "who is to come," and thus signifies from eternity to eternity.

[2] That "Is," signifies from eternity is also known in the Christian world from the Psalm of David, where it is said:

I will declare of the decree; Jehovah said unto me; thou art My son; this day have I begotten thee (Psalm 2:7);

it is known that these things are said of the Lord, and that by "today" is meant from eternity. (That by "tomorrow," also in the Word, where the Lord is treated of, is signified to eternity, see Arcana Coelestia, 3998.) That the words "who is," "who was," and "who is to come," signify also the All in all things of heaven and the church is because they signify eternity; and in heaven eternity can be expressed by no other word than Divine, for the reason that what is infinite cannot fall into the angelic idea, and still less into a human idea; and eternity is infinite Existere from infinite Esse; but only this enters the idea, that eternity, which is the Divine in respect to Existere, is the All in all things of heaven and of the church. For the whole heaven is heaven not from the angels' proprium [selfhood, or what is their own], but from the Divine of the Lord; nor is the church the church from the proprium of men, but from the Divine of the Lord; for all the good of love and the truth of faith are from the Lord, and it is the good of love and the truth of faith that make heaven and the church. Angels and men are only recipients, and so far as they receive, heaven and the church are in them. (These things may be seen illustrated by many things in the work on Heaven and Hell, 7-12, where it is shown that the Divine of the Lord makes heaven, and that the Divine that makes heaven is the Divine Human, which is the Divine Existere from the Divine Esse, 78-86)