Zechariah 12:10 contains the stunning promise: "They will look to me whom they have pierced." The Apostle John provides the definitive interpretation in John 19:37, noting that this was fulfilled when the Roman soldier pierced Jesus’ side with a spear.
The speaker in Zechariah 12 is Yahweh. Therefore, when Jesus is pierced, it is God Himself participating in the suffering of His people to secure their redemption. This moment was the "opening of the fountain" (Zechariah 13:1) that allowed the spirit of grace to be poured out on the house of David at Pentecost.