pour out: This term describes God pouring out the spirit of prophecy on Israel and all people on the day of the Lord (compare Ezekiel 39:28–29; Joel 2:28–29) and God's judgment on the wicked (Lamentations 2:4; Hosea 5:10; Zephaniah 3:8).
spirit of grace: God's undeserved and unsolicited favor encourages people to seek Him through humble and repentant prayer (see Psalm 86:15–16).
the One they have pierced: The New Testament views the piercing of God as a reference to the piercing of the Messiah, Jesus of Nazareth (John 19:34–37; Revelation 1:7).