Horses going in and out of heaven have been prophesied several times. Horses are also normally used for battles.....and we know that God has His army.
Joel 2:11
The LORD thunders at the head of his army; his forces are beyond number, and mighty is the army that obeys his command. The day of the LORD is great; it is dreadful. Who can endure it?
So, I don't think this is metaphorical.
2 Kings 2:11
11 As they were walking along and talking together, suddenly a chariot of fire and horses of fire appeared and separated the two of them, and Elijah went up to heaven in a whirlwind.
2 Kings 6
17 And Elisha prayed, “Open his eyes, Lord, so that he may see.” Then the Lord opened the servant’s eyes, and he looked and saw the hills full of horses and chariots of fire all around Elisha.
Revelation 6
The Seals
6 I watched as the Lamb opened the first of the seven seals. Then I heard one of the four living creatures say in a voice like thunder, “Come!” 2 I looked, and there before me was a white horse! Its rider held a bow, and he was given a crown, and he rode out as a conqueror bent on conquest.
3 When the Lamb opened the second seal, I heard the second living creature say, “Come!” 4 Then another horse came out, a fiery red one. Its rider was given power to take peace from the earth and to make people kill each other. To him was given a large sword.
5 When the Lamb opened the third seal, I heard the third living creature say, “Come!” I looked, and there before me was a black horse! Its rider was holding a pair of scales in his hand. 6 Then I heard what sounded like a voice among the four living creatures, saying, “Two pounds[a] of wheat for a day’s wages, and six pounds[c] of barley for a day’s wages,[d] and do not damage the oil and the wine!”
Zechariah 1
The Man Among the Myrtle Trees
7 On the twenty-fourth day of the eleventh month, the month of Shebat, in the second year of Darius, the word of the Lord came to the prophet Zechariah son of Berekiah, the son of Iddo.
8 During the night I had a vision, and there before me was a man mounted on a red horse. He was standing among the myrtle trees in a ravine. Behind him were red, brown and white horses.
9 I asked, “What are these, my lord?”
The angel who was talking with me answered, “I will show you what they are.”
10 Then the man standing among the myrtle trees explained, “They are the ones the Lord has sent to go throughout the earth.”