Zechariah's Explanation
Apostle John who was with Christ until his last moment of the crucifixion, has revealed that Jesus Christ is not the image of Word alone, but the Image of Father, Word and the Holy Spirit, and we must believe in him to overcome this world - 5.Who is it that overcomes the world? Only the one who believes that Jesus is the Son of God. 6.This is the one who came by water and blood—Jesus Christ. He did not come by water only, but by water and blood. And it is the Spirit who testifies, because the Spirit is the truth - 1 John 5:5-6
To understand this in a better way, apostle John first explaining the Trinity of our Heavenly Father as Father, Word and Holy Spirit - because there are three who are testifying in Heaven: the Father, the Word, and the Holy Spirit, and these three are one - 1 John 5:7
And then he explained about the Son Jesus Christ, that Jesus had all three of them(Father, Son, and the Holy Spirit) in him - and there are three who are testifying in the earth: the Spirit(Holy Spirit), and the water(Word), and the blood(Father) and the three are into the one(Jesus Christ) - 1 John 5:8
That was the reason Apostle Paul is saying that Jesus Christ is the Image of the invisible God - The Son is the image of the invisible God, the firstborn over all creation - Colossians 1:15 that means in Jesus Christ we can see the Son (The Word became flesh - John 1:14), and our Heavenly Father (Father is in me - John 10:38), and the Holy Spirit (Spirit of the Lord is upon me - Luke 4:18).
Zechariah's Explanation
before going over Zechariah's explanation about the Trinity God, we need to understand about the usage of word horse in the Bible, Horse is the one of the fastest animal in the world, but in the Bible, its used for referring to the Spirit that we can see in this passage - the Egyptians are man, and not God, and their horses are flesh, and not spirit - Isaiah 31:3
When horses are referring to the Spirit of the Man, the rider of the horse is referring to his physical body - On that day, declares the Lord, I will strike every horse with panic, and its rider with madness. But for the sake of the house of Judah I will keep my eyes open, when I strike every horse of the peoples with blindness - Zechariah 12:4
But in Zechariah's vision Horses are pointing to Spirit of God, and his vision starts like this - 8.I saw in the night, and behold, a man riding on a red horse! He was standing among the myrtle trees in the glen, and behind him were red, sorrel, and white horses. 9.Then I said, What are these, my lord? The angel who talked with me said to me, I will show you what they are - Zechariah 1:8-9
Here the red horse which standing among the myrtle trees in the glen alone had the rider on it, and is referring our Savior and Lord Jesus Christ, and the Myrtle trees in the glen is referring to the people of this world
That was the reason, prophet Zechariah called the rider of the red horse as Lord(Jesus Christ), and the rider of the red horse also referred as Angel that we can see across the Old Testament.
And behind him were red, sorrel, and white horses, which are referring to our God of Trinity (Father, Word, and the Holy Spirit), and these three horses does not have any riders, that means they do not have any physical appearance, and its a character of our unseen God.
And prophet Zechariah could only talk to our Mediator Jesus Christ, and not directly to the God of Trinity (Father, Word, and the Holy Spirit).
We can see that the Angel of the Lord(Jesus Christ) calling the three horses as O Lord of Hosts, which confirms that the three horses are referring to our God of Trinity (Father, Word, and the Holy Spirit) - 10.So the man who was standing among the myrtle trees answered, ‘These are they whom the Lord has sent to patrol the earth. 11.And they answered the angel of the Lord who was standing among the myrtle trees, and said, We have patrolled the earth, and behold, all the earth remains at rest. 12.Then the angel of the Lord said, O Lord of hosts, how long will you have no mercy on Jerusalem and the cities of Judah, against which you have been angry these seventy years? - Zechariah 1:10-12
The conversation between the person who is standing among the myrtle trees and the three Horses confirms what the horses are representing - 13.And the Lord answered gracious and comforting words to the angel who talked with me. 14.So the angel who talked with me said to me, Cry out, Thus says the Lord of hosts: I am exceedingly jealous for Jerusalem and for Zion. 15.And I am exceedingly angry with the nations that are at ease; for while I was angry but a little, they furthered the disaster. 16.Therefore, thus says the Lord, I have returned to Jerusalem with mercy; my house shall be built in it, declares the Lord of hosts, and the measuring line shall be stretched out over Jerusalem. 17.Cry out again, Thus says the Lord of hosts: My cities shall again overflow with prosperity, and the Lord will again comfort Zion and again choose Jerusalem - Zechariah 1:10-17
How God revealed Jesus Christ and the Trinity of our Heavenly Father as 4 horses, the same way he also showed Satan's plan(4 horns) to prophet Zechariah - 18.And I lifted my eyes and saw, and behold, four horns! 19.And I said to the angel who talked with me, What are these? And he said to me, These are the horns that have scattered Judah, Israel, and Jerusalem.
But the Son of God, and the Trinity God working together as four craftsmen for our Salvation, and victory belongs to our Lord Jesus Christ - 20.Then the Lord showed me four craftsmen. 21.And I said, What are these coming to do? He said, These are the horns that scattered Judah, so that no one raised his head. And these have come to terrify them, to cast down the horns of the nations who lifted up their horns against the land of Judah to scatter it
Prophet Zechariah have received this wonderful vision so that we can understand the Father, Son and Holy Spirit, but not to make any curved images - God is spirit, and those who worship him must worship in spirit and truth - John 4:24 & You shall not make for yourself a carved image, or any likeness of anything that is in heaven above, or that is in the earth beneath, or that is in the water under the earth - Exodus 20:4
Joel's Explanation
Prophet Joel also used horses to refer the Spirit of God, and explained the Trinity of Jesus Christ using three different types of noise that horses would make in the war zone - 4.The appearance of them is as the appearance of horses; and as horsemen, so shall they run. 5.With a noise like chariots Over mountaintops they leap, Like the noise of a flaming fire that devours the stubble, Like a strong people set in battle array - Joel 2:4-5
Habakkuk's Explanation
When Prophet Habakkuk spoke about Christ's crucifixions, He prophesied as horses getting into the great water, but he used plural term(horses) to revel the Trinity of our Lord Jesus Christ - 8.O Lord, were You displeased with the rivers, Was Your anger against the rivers, Was Your wrath against the sea, That You rode on Your horses, Your chariots of salvation? 9.Your bow was made quite ready; Oaths were sworn over Your arrows. Selah 10.You divided the earth with rivers. The mountains saw You and trembled; The overflowing of the water passed by. The deep uttered its voice, And lifted its hands on high. 11.The sun and moon stood still in their habitation; At the light of Your arrows they went, At the shining of Your glittering spear. 12.You marched through the land in indignation; You trampled the nations in anger. 13.You went forth for the salvation of Your people, For salvation with Your Anointed. You struck the head from the house of the wicked, By laying bare from foundation to neck. Selah. 14.You thrust through with his own arrows The head of his villages. They came out like a whirlwind to scatter me; Their rejoicing was like feasting on the poor in secret. 15.You walked through the sea with Your horses, Through the heap of great waters - Habakkuk 3:8-15