Zechariah 12:10a says, "I will pour out on the house of David and on the inhabitants of Jerusalem the Spirit of grace and of supplications; and they will look upon Me, whom they have pierced." In Acts 2 God poured out His Spirit upon all flesh (v. 17), and three thousand were saved. But when God pours out the Spirit of grace upon the inhabitants of Jerusalem, many thousands of Israel, even the entire race of Israel, will be saved.
The Spirit of grace in Zechariah 12:10 is a sweet term, and is in contrast to the Spirit of power in Acts 1:8 and 2:1-4. We should experience the Spirit both as the Spirit of power and as the Spirit of grace. The Spirit of power is to strengthen us, but the Spirit of grace is to bring us into the enjoyment of the Triune God. In Acts 2 there was the participation in the divine power through the Holy Spirit, but there was not that much enjoyment of the Triune God. In Acts 2, at the beginning of the age of grace, the church age, the Spirit was mainly the Spirit of power. But in Zechariah 12, at the ending, the consummation, of the age of grace, the Spirit will be mainly the Spirit of grace for the enjoyment of the Triune God.
By the time of the Lord's second appearing, the remnant of Israel will have suffered all kinds of hardship. They suffered the destruction of Jerusalem in A.D. 70 and were scattered to other countries. In these other countries they continued to suffer persecution. Today most of the Jews remain in dispersion, but many are returning to the nation of Israel. At the time of Antichrist, two-thirds in all the land of Israel will be slaughtered (13:8-9a). Half of the city of Jerusalem will go forth into captivity (14:2). The half which remains will no longer have any taste for human life or for acquiring possessions and high positions. They will realize that they are short of God and will exercise their spirit (12:1), not their mind. At this juncture they will repent, because they have lost their taste for everything. The Holy Spirit will be poured out upon them, and they will follow their spirit to be fully occupied with God. I believe that because they will have learned that everything apart from God is vanity and because they will exercise their spirit, the pouring out of the Spirit of God upon them will be intensified. The Jews on the day of Pentecost were stubborn and hard. Hence, the Spirit of power was poured out to inspire them to repent. But the inhabitants of Jerusalem in Zechariah 12:10 will have already repented; therefore, the Spirit of grace will be poured out upon them so that they can receive the Triune God as their enjoyment.
Zechariah 12:10a also tells us that they will look upon Him whom they have pierced. This means that they will look upon the Christ who was pierced by them. Revelation 1:7a refers to this: "Behold, He comes with the clouds, and every eye will see Him, even those who pierced Him." The piercing of Christ is the foundation of redemption. Apart from Christ's being pierced, there would be no base for our redemption.
The repentant Jews will look upon the One whom they have pierced. Although it was their forefathers who pierced the Lord Jesus, God counts that as something done by these repentant ones. The reason for this is that in the sight of God the entire people of Israel is one person.