"Spiritual, or heavenly
horses represent judgment, and usually dramatic judgment for the sake of violent purification. They are a portent of bad things to come. In scripture, the symbolic horse generally represents a particular aspect or agent of punishment or plague. In Rev 6, we get a taste of things to come in terms of horses riding out with the first "seals".
In Rev 19:11-15, Jesus appears in ultimate judgment on a white horse with "His robe dipped in blood", a violent and fearsome image of God's ultimate purging wrath being poured out on rebellious mankind. The following verses should give the gist.
Zec 1:8 (NIV) During the night I had a vision--and there before me was a man riding a red horse! He was standing among the myrtle trees in a ravine. Behind him were red, brown and white horses. I asked, "What are these, my lord?" The angel who was talking with me answered, "I will show you what they are." Then the man standing among the myrtle trees explained, "They are the ones the Lord has sent to go throughout the earth." ...This is what the Lord Almighty says: 'I am very jealous for Jerusalem and Zion, but I am very angry with the nations that feel secure. I was only a little angry, but they added to the calamity.'" ...Then I looked up--and there before me were four horns! I asked the angel who was speaking to me, "What are these?" He answered me, "These are the horns that scattered Judah, Israel and Jerusalem."
Zec 14:12-20 (NIV) This is the plague with which the Lord will strike all the nations that fought against Jerusalem: Their flesh will rot while they are still standing on their feet, their eyes will rot in their sockets, and their tongues will rot in their mouths. On that day men will be stricken by the Lord with great panic. Each man will seize the hand of another, and they will attack each other... A similar plague will strike the horses and mules, the camels and donkeys, and all the animals in those camps. Then the survivors from all the nations that have attacked Jerusalem will go up year after year to worship the King, the Lord Almighty... This will be the punishment of Egypt and the punishment of all the nations that do not go up to celebrate the Feast of Tabernacles. On that day HOLY TO THE Lord will be inscribed on the bells of the horses, and the cooking pots in the Lord's house will be like the sacred bowls in front of the altar."