In Zechariah 12, the prophet has an oracle concerning a future invasion of Judah and Jerusalem. But, he says, the tables will be turned against Judah's enemies: Jerusalem would be a "cup of staggering" (12:2) and Judah a "flaming torch among sheaves" (6): small, but it will consume the nations that surround it.
God is a warrior. He fights for Israel - saving Judah first because of their dependence on Jerusalem, and protecting Jerusalem itself. God's power is such that Jerusalem's weakest citizen will be, as it were, a warrior like David. And thus will God destroy the enemies of his chosen people.
And then, Zechariah says, God will pour out a grace upon them the like of which they have not seen, and Jerusalem and the house of David will "look on me, on him whom they have pierced," and they will mourn, like one mourns over the death of a child (12:10). The sins of the nation are as if they have run God himself through with a spear. But even when they forgot him, he did not forget them, and he will grant them the grace of repentance.
Five hundred years later, the John witnessed the crucifixion of Jesus. He saw his rabbi, whom he had followed for three years, run through by the spear of a Roman soldier. And John writes that Zechariah 12:10 was fulfilled in that act: "they will look on him whom they have pierced" (John 19:37). As he died, Jesus was looked upon by his kinsmen, his mother and her sister; and his friends, Mary Magdalene, John, and others who knew him and watched from a distance. Whether Jesus' other disciples were present isn't specifically said. It seems unlikely. Some of the rulers were th ere too, mocking Jesus and taunting him to save himself (Luke 23:35). Literally, he was looked upon by his fellow countrymen who pierced him. Some of them, like Joseph of Arimathea, looked upon him with penitence instead of scorn.
But this time of mourning has not yet come for the Jews, although a few of them have turned to Christ, along with untold Gentiles. This situation led Paul to ponder whether the promises of God had failed (Rom. 9:1-6) No, he concluded: some had obtained them, but the rest were hardened (Rom. 11:7), and because of their stubbornness God's grace had come instead to the Gentiles for a time. But once the Gentiles have been brought into the Church, God's mercy will come again to his people Israel (Rom. 11:25).
The time will come when all the families of Israel will look upon Jesus their Messiah and mourn for their sins. That time is not yet. It is, I pray, not far away.