The difficulty of interpreting this passage stems from the phrase “on that day” used three times in these verses. Adamant premillennialists take this to be a reference to the era before the second advent ushering in the millennium. I think this refers to the first advent of Christ. The first reference to “on that day” in v. 1 clearly refers to Christ’s shedding of His blood for the redemption of His people. As they mourned the one whom they pierced (12:10), so God will open for them a fountain “to cleanse them from sin and uncleanness.” Even dispensationalists admit that this clearly refers to Calvary but believe the promise of this verse has yet to be fulfilled.
We can reasonably conclude that if the first reference to “on that day” refers to Christ’s work on the cross (at His first advent), then it seems entirely appropriate to assume the other two “on that day” references also denote the first coming of Christ. Using the language and imagery contemporary readers would have understood, the effect of Christ’s coming, death and resurrection is to cleanse His people from the two major sins which always plagued Israel, namely, idolatry (v. 2) and false prophets (“spirit of uncleanness” v. 2). God’s people will be discerning enough to root out the false prophets. Baal worshippers often cut themselves (cf. the prophets of Baal on Mt. Carmel in 1Kings); those false prophets will be exposed and cut off.
This does not mean that the New Covenant community will never face false prophets or teachers (they will continue to exist and molest the people of God, 1Jn. 4:1) but because we have the anointing to teach us all things (1Jn. 2:26-27) as prophesied in terms of the New Covenant (“they shall all know me” Jer. 31:34), we will be better equipped to recognize and resist them. Webb suggests that this was written “to assure us that on the last day all lying in God’s name and all compromising with the truth on the part of his people will be over.”
Before our Lord was betrayed, Jesus told his disciples that they will fall away from him and he cited v. 7 (Mt. 26:31, 32). This verse therefore refers to Jesus Christ. Whereas in ch. 12, Israel will mourn for the one they pierced, here God is the one who strikes the Shepherd, the Lord Jesus. It is God (“Declares the Lord of hosts”) who says “Awake, O sword, against my shepherd, against the man who stands next to me [that is, God].” The “sword” represents the Lord’s own judgment against His Son and it will scatter and purify the sheep (vv. 8-9).
Some believe vv. 8-9 refer to the ethnic Israelites for the future in the “great tribulation,” just before the supposed Messianic age (i.e. Millennium). Surely what is said here in vv. 8-9 refers to God’s new covenant people. They will be refined; over time, through persecution, trials, difficulties, adversities, etc. the Lord will have His people persevere. Remember, it is the one who endures unto the end who shall be saved. The glorious future of God’s people (already mentioned in Zechariah) must be seen in conjunction with her afflictions (cross before glory).
Malachi also mentions this refining: “But who can endure the day of his coming, and who can stand when he appears? For he is like a refiner’s fire and like fullers’ soap. 3 He will sit as a refiner and purifier of silver, and he will purify the sons of Levi and refine them like gold and silver, and they will bring offerings in righteousness to the LORD.” (Mal. 3:2, 3) Zechariah’s vision of the future accords with Malachi’s.
The prophecy ends this chapter with the comforting words of covenant promises: The refining will enable His tested people to call upon God. God will declare them to be His people and they will say, “The Lord is my God.”
Lesson: The Lord knows those who are His and through the refining, all God’s children will persevere. God will own us because He has saved us through our Lord Jesus Christ.
 Kenneth Barker (EBC Revised) admits that New Covenant community of Jews and Gentiles received the “benefits promised to Israel.” That is, we only received the benefits of this by God’s grace but we are not the heirs of these promises in Christ. He says, “These blessings will yet be experienced by ethnic Israel at the second advent of their Messiah (Ro 11:25–29)…” See Kenneth L. Barker, “Zechariah,” in Daniel-Malachi (vol. 8 of The Expositor’s Bible Commentary Revised Edition, ed. Tremper Longman III and David E. Garland; Accordance electronic ed. Grand Rapids: Zondervan, 2008), 819. M. Unger says that the “cleansing fountain was opened potentially for Israel and the whole world. But because Israel has rejected this fountain, it will not be open to her experientially until in that [future] day…” (Zechariah: Prophet of Messiah’s Glory, 222).
 Webb, The Message of Zechariah, 167.
 M. Unger, Zechariah: Prophet of Messiah’s Glory, 235.
 For example, K. Barker in the EBC Revised series.
 Cf. Michael Bentley, Building for God’s Glory (Haggai & Zechariah), Welwyn Commentary Series (Durham: Evangelical Press, 1989), 212.