Zechariah is a book of prophecy. Much of it has been fulfilled—precisely. The rest of it is yet to be fulfilled just as precisely. It is as though the prophet were looking across a landscape. He could see the fields of flowers at the top of the ridge, and the mountain peaks in the distance. But, from his viewpoint, the scenes blended together so that they ran together into one.
Zechariah 9:9 was the some distance away from him:
Rejoice greatly, Daughter Zion!
Shout in triumph, Daughter Jerusalem!
See, your King is coming to you;
He is righteous and victorious,
humble and riding on a donkey,
on a colt, the foal of a donkey.
Jesus fulfilled this prophecy as He made His triumphant entrance into Jerusalem.
Zechariah 9:10 was a much greater distance away:
I will cut off the chariot from Ephraim
and the horse from Jerusalem.
The bow of war will be removed,
and He will proclaim peace to the nations.
His dominion will extend from sea to sea,
from the Euphrates River
to the ends of the earth.
This is yet future, yet to be fulfilled.
We must remember that when we read the Bible there are two aspects to prophecy. There is that which has already been fulfilled, and there is that which is yet to be fulfilled. But, to the prophet, both were still future. But the point is this: as we looked back at those completed prophecies we can see they came true exactly. We may be sure that those prophecies that have not yet been fulfilled will come true just as completely.