Zechariah 12 begins with a siege of Jerusalem (12:3), but the Lord promises that He will intervene to save Judah and Jerusalem (vv. 6-9). In Zechariah 12:10-13:1: the siege has been lifted, and during this respite, the Lord promises to pour out His Spirit upon the house of David and inhabitants of Jerusalem.
The effect of the pouring out of the Spirit is mourning. What instigates the mourning is that they look on “Me,” the Lord, whom they have pierced (v. 10). More specifically, the verse must be talking about the rejected shepherd of chapter 11. He too was identified with the Lord, and he too was “gored” by the people’s rejection. The Lord, in the person of the shepherd, is pierced, spurned and rejected by His people. Now, the people mourn because they have rejected and despised Him. Specifically, the leaders of Jerusalem and the royal house of David, who were responsible for piercing the shepherd, mourn.
The mourning described by series of comparisons.
It is like the mourning for an only child, perhaps a reference to Issac. Isaac is the “covenant incarnate,” the pierced one is likewise the covenant representative of the people. The mourning over the firstborn is also like the mourning of the Egyptians at the time of Passover (Ex 12:29-30). Zechariah describes in detail how each family, from the royal and priestly families on down, was affected by the death of the pierced one. The same is said of Passover: there was mourning in every house, because there was death in every house. Zechariah, in other words, says that it will be like Passover, but a strange Passover. It is not the firstborn of Egypt that has died, but the firstborn of Israel. In fact, the Lord’s own firstborn has died like an Egyptian. It is not Egyptians mourning, but Jews. It is not the angel of death who killed the firstborn, but the Jews themselves.
Those filled with the Spirit recognize what has happened. The Good Shepherd was indeed another Josiah, and the Jews’ rejection of His ministry sealed their doom. The fountain for the house of David and the inhabitants of Jerusalem is a promise of repentance and cleansing. Despite the hymns about fountain filled with blood, this is a fountain filled with water. The water referred to here is the water for impurity in Numbers 19, made from the ashes of a red heifer, cedar wood, hyssop, and scarlet, and concocted into into water that removes “impurity ( niddah ). According to Numbers 19:9, this cleanses people from contact with the dead. Zechariah prophesies of a time when there will be a continual, uninterrupted flow of cleansing water, of water that will cleanse people from contact with the corpse, the corpse of the shepherd. In context, the fountain of water is parallel to the Spirit, who is the true water of cleansing.