To "declare" means to say something formally, publicly and with emphasis; you might say what you think, but you only declare things you're sure of. So just as saying relates to sharing truth at various levels, "declaring" relates to sharing fundamental, unquestioned principles, often those that reveal the Lord and the salvation that lies in His embrace.

In Amos 4:12-13, 'to declare' signifies to flow in.

(References: Apocalypse Revealed 478; Arcana Coelestia 7550, 8762)

478. The mystery of God would be concluded, as He declared to His servants the prophets. This symbolically means that then will appear what was foretold in the Word of both Testaments and previously concealed, that after the Last Judgment upon those people who have destroyed the church, the Lord's kingdom will come.

To be concluded means, symbolically, to be fulfilled, to come to an end, and then to reappear. The mystery of God declared to the prophets symbolizes something foretold by the Lord in the Word and previously concealed. To declare good news means, symbolically, to proclaim the coming of the Lord and His kingdom, for the gospel is happy news. That this would come about after the Last Judgment was executed on the people who destroyed the church was also foretold in the Word. Therefore this, too, is symbolically meant.

It can be seen from this that all of these meanings are contained in these words.

[2] First we must say something here about the Lord's advent and His kingdom's being foretold in the Word of both Testaments:

In the Word of the Old Testament, in the spiritual sense of the prophetic portion, and also in its natural sense wherever the spiritual sense shines through, the subject is the Lord alone, namely, His advent in the fullness of time, a time when the goodness of charity and the truth of faith would no longer be present in the church, whose state then is called a consummation, a being laid waste, a desolation, and a cutting off. It includes as well His battles with the hells and victories over them, which constitute also the last judgment that He executed, and after that the creation of a new heaven and the establishment of a new church, which are the Lord's kingdom to come. All of this is found in the Word of the New Testament, too, in the portion called the Gospels, and in particular in the book of Revelation.

[3] That it is the Lord's kingdom that would be declared in the days of the sounding of the seventh angel is apparent in the next chapter (chapter 11) from the following:

Then the seventh angel sounded: and there were loud voices in heaven, saying, "The kingdoms of this world have become the kingdoms of our Lord and of His Christ, and He shall reign forever and ever!" And the twenty-four elders... fell on their faces and worshiped God, saying, "We give You thanks, O Lord God..., who are and who were and who are to come, because You have taken Your great power and reigned. (Revelation 11:15-17)

[4] This mystery, in almost the same words as in Revelation here, is described in Daniel, where we find the following:

I heard the man clothed in linen..., when he held up his (hands) to heaven, and swore by Him who lives forever, that it shall be for a set time of set times and a half..., when... all these things shall be finished... But he said, "Go your way, Daniel, for the words are closed up and sealed till the time of the end." (Daniel 12:7, 9)

Till the time of the end refers to the present time. That the Son of Man would then receive His kingdom - this Daniel foretells in these words:

I was watching in the night visions, and behold, One like the Son of Man, coming with the clouds of heaven! ...Then to Him was given dominion and glory and a kingdom, and all peoples, nations, and languages will worship Him. His dominion is an everlasting dominion, which shall not pass away, and His kingdom one which shall not perish. (Daniel 7:13-14)

[5] That declaring good news symbolizes the Lord's advent and His kingdom then, is apparent from the following passages:

Get up into the... mountain, O Zion, who brings good tidings; lift up your voice with strength, O Jerusalem, who brings good tidings... Say..., "Behold your God!" Behold, the Lord Jehovih is coming with strength, and His arm shall rule for Him. (Isaiah 40:9-10)

How delightful upon the mountains are the feet of him who brings good news, who proclaims peace, who brings glad tidings of goodness, who proclaims salvation, who says to Zion, "Your King shall reign!" (Isaiah 52:7, cf. Nahum 1:15)

Sing to Jehovah, bless in His name; proclaim the good news of His salvation from day to day... ...Jehovah, for He is coming... (Psalms 96:2, 13)

The Spirit of the Lord Jehovih is upon Me; therefore Jehovah has anointed Me to bring good tidings to the poor..., to proclaim liberty to the captives..., to proclaim the year of Jehovah's good pleasure... (Isaiah 61:1-2)

The angel said to (Zacharias), "(Behold)..., your wife... will bear... a son..., (who) will go before (the Lord God) in the spirit and power of Elijah..., to prepare a people for the Lord... I am Gabriel..., and I was sent... to bring you these glad tidings." (Luke 1:13, 17, 19)

...the angel said to (the shepherds), "Do not be afraid, ...behold, I bring you good tidings of great joy... For there is born to you this day in the city of David a Savior, who is Christ the Lord." (Luke 2:10-11)

The Lord brought good tidings of the kingdom of God: Matthew 4:23; 9:35; Mark 1:14-15. So did John the Baptist: Luke 3:18.

The Lord also said to the Disciples,

Go into all the world and proclaim the good news to every creature. (Mark 16:15)

This, too, is the everlasting good news or gospel that "the angel flying in the midst of heaven" had "to proclaim to the those who dwell on the earth" (Revelation 14:6).

[6] Our being told that the mystery of God would be concluded means that something would be fulfilled that was not fulfilled before, namely, the coming of the Lord's kingdom. It was not fulfilled by the Jews because they did not acknowledge the Lord. Neither has it been fulfilled by Christians because they do not acknowledge the Lord to be God of heaven and earth even in respect to His human element; for they regard this as being like anyone else's human element. Consequently they do not turn to Him directly, even though He is Jehovah who came into the world.