Short answer, talking all the prophetic symbolism into account it speaks of Christ's coming into the world to redeem His people and establish His kingdom. Both of these things He accomplished at His first coming, although there is an ongoing work of building the kingdom.
I believe it all fits with the teaching that the "law and prophets" all pointed to Christ. If you understand the apocalyptic language it makes sense, esp. in light of how the NT authors interpreted the prophets.
Topcat, here is where we have a rub. You have a tendency to too broadly symbolize what the text is saying to try to make it fit your soteriology. Zechariah 12-14 is very specific. It speaks of Jerusalem being encompassed about. It speaks of her spoil being divided in her midst. It also speaks of Jesus coming to fight for her and literally splitting the mount of olives. It is all set in Israel. And, I do not see how any of it was accomplished at His first coming. The vast majority of Jews are still lost and His kingdom was to be earthly in addition to Heavenly as we see in other Scriptures.