This section of Zechariah continues the prophecies from the previous chapter. These prophecies are not in chronological order; they are looking at the same event from different perspectives.
In Chapter 12:1-9, there is a prophecy about an event that will occur "in that day" (v.3). What is the day being referred to here? This can be identified as the day of the Lord Jesus Christ. The day of His coming and establishing His kingdom marked the fulfillment and bringing to an end of the Old Covenant.
The blessing on Israel as a physical nation was ended. The New Covenant spiritual Israel is what is in view in this chapter -- a kingdom that will be trembled at.
There is a blessing here on the house of David. Christ, the seed of David, will be exalted. All of His followers will have the courage and strength to overcome trouble and testing in that day.
Verses 10 and 11 give a better understanding of that day -- it is the day when they will look upon Christ and see Him pierced (His death on the cross).
Verses 12-14 describe a mourning. This will not be a national mourning, but rather a particularized mourning. It is an individual thing, as the New Covenant is made up of individuals. Individuals must each mourn their sin and the death of their Savior by themselves.
Chapter 13:1 identifies the Lord Jesus' death on the cross. He is the fountain opened for sin and uncleanness.
Verses 2-6 describe the result of the finished work of Christ. No false teaching will be tolerated in the Kingdom. People will recognize the truth and tolerate nothing that diminishes Christ's glory. Apostles and prophets will demand truth and will refuse to hear false prophets. False prophets will repent and be corrected and ashamed of their false teaching. They will be brought to repentance by their friends.
Verses 7-9 are a section that Jesus quoted. God smote the Shepherd; He slayed His only Son and the sheep were scattered. Note that two thirds were cut off -- but a remnant was saved.