The speaker identifies himself as the Lord of [heaven's] armies aka Michael the mighty ruler aka the Messiah/Christ and the pre-incarnate Jesus. If I am wrong on that point then my answer will require some tweaking to Michael being associated with the Angel of the LORD but not the Angel of the LORD. But to keep things simple I'll assume they are all the same person.
The Angel of the LORD suggests there will come a day when the saints would assemble for a battle with the angelic army.
In the epistle of Jude, Jude cites the scrolls of Enoch:
[Jde 1:14 NASB] (14) It was also about these men that Enoch, in the seventh generation from Adam, prophesied, saying, "Behold, the Lord came with many thousands of His holy ones,
9 And behold! He cometh with ten thousands of His holy ones
To execute judgement upon all,
And to destroy all the ungodly:
And to convict all flesh
Of all the works of their ungodliness which they have ungodly committed,
And of all the hard things which ungodly sinners have spoken against Him.
There is no other canonical indication that it was Enoch that made this prediction. Instead we see it on the lips of Moses:
[Deu 33:1-3 NASB] (1) Now this is the blessing with which Moses the man of God blessed the sons of Israel before his death. (2) He said, "The LORD came from Sinai, And dawned on them from Seir; He shone forth from Mount Paran, And He came from the midst of ten thousand holy ones; At His right hand there was flashing lightning for them. (3) "Indeed, He loves the people; All Your holy ones are in Your hand, And they followed in Your steps; Everyone receives of Your words.
In at least this version of the LXX, "holy ones" becomes "Cades", a place named "holiness" and it is the angels who are with him:
LXX2012(i) 1 And this [is] the blessing with which Moses the man of God blessed the children of Israel before his death. 2 And he said, The Lord is come from Sina, and has appeared from Seir to us, and has hasted out of the mount of Pharan, with the ten thousands of Cades; on his right hand [were] his angels with him. 3 And he spared his people, and all his sanctified ones [are] under your hands; and they are under you; and he received of his words
But in addition, all his "holy ones" are "under your hands" and "they are under you", perhaps word that can refer to being soldiers along with the angels.
Many undertake to determine the timing of "the rapture" but fail to consider the prophetic origin of the idea, which is what I take this passage, in conjunction with Zechariah 3:7, to be. See also:
[1Ki 22:19 NASB] (19) Micaiah said, "Therefore, hear the word of the LORD. I saw the LORD sitting on His throne, and all the host of heaven standing by Him on His right and on His left.
[Mat 16:27 NASB] (27) "For the Son of Man is going to come in the glory of His Father with His angels, and WILL THEN REPAY EVERY MAN ACCORDING TO HIS DEEDS.
[Mat 25:31-34, 46 NASB] (31) "But when the Son of Man comes in His glory, and all the angels with Him, then He will sit on His glorious throne. (32) "All the nations will be gathered before Him; and He will separate them from one another, as the shepherd separates the sheep from the goats; (33) and He will put the sheep on His right, and the goats on the left. (34) "Then the King will say to those on His right, 'Come, you who are blessed of My Father, inherit the kingdom prepared for you from the foundation of the world. ... (46) "These will go away into eternal punishment, but the righteous into eternal life."
These tens of thousands of saints are also the identity of the 144,000 (12,000 from each of 12 tribes) who are his first fruits:
[Rev 14:1, 3 NASB] (1) Then I looked, and behold, the Lamb was standing on Mount Zion, and with Him one hundred and forty-four thousand, having His name and the name of His Father written on their foreheads. ... (3) And they sang a new song before the throne and before the four living creatures and the elders; and no one could learn the song except the one hundred and forty-four thousand who had been purchased from the earth.
[Rev 19:11-16 KJV] (11) And I saw heaven opened, and behold a white horse; and he that sat upon him was called Faithful and True, and in righteousness he doth judge and make war. (12) His eyes were as a flame of fire, and on his head were many crowns; and he had a name written, that no man knew, but he himself. (13) And he was clothed with a vesture dipped in blood: and his name is called The Word of God. (14) And the armies which were in heaven followed him upon white horses, clothed in fine linen, white and clean. (15) And out of his mouth goeth a sharp sword, that with it he should smite the nations: and he shall rule them with a rod of iron: and he treadeth the winepress of the fierceness and wrath of Almighty God. (16) And he hath on his vesture and on his thigh a name written, KING OF KINGS, AND LORD OF LORDS.
It is to this that Jesus refers in his promise:
[Rev 3:4 NLT] (4) "Yet there are some in the church in Sardis who have not soiled their clothes with evil. They will walk with me in white, for they are worthy.
In contrast to:
[Jer 21:5 NLT] (5) I myself will fight against you with a strong hand and a powerful arm, for I am very angry. You have made me furious!
So to summarize, Zechariah seems to be picking up on Enoch's prophecy on the lips of Moses that the worthy will one day join ranks with the Messiah and his angels, a theme somewhat ubiquitous in the NT.