Zechariah: 12:10-11  "And I will pour on the house of David and on the inhabitants of Jerusalem the Spirit of grace and supplication; then they will look on Me whom they pierced. Yes, they will mourn for Him as one mourns for his only son, and grieve for Him as one grieves for a firstborn. 11 "In that day there shall be a great mourning in Jerusalem, like the mourning at Hadad Rimmon in the plain of Megiddo."

Here, it is foretold that Christ should be pierced, and this scripture is quoted as that which was fulfilled when Christ’s side was pierced upon the cross (John 19:36-37 "36 For these things were done that the Scripture should be fulfilled, "Not one of His bones shall be broken." 37 And again another Scripture says, "They shall look on Him whom they pierced.)

He is spoken of as one whom we have pierced; it is spoken primarily of the Jews, who persecuted him to death (and we find that those who pierced him are distinguished from the other kindreds of the earth that shall wail because of him, (Rev. 1:7); yet it is true of us all as sinners, we have pierced Christ, inasmuch as our sins were the cause of his death, for he was wounded for our transgressions, and they are the grief of his soul; he is broken with the whorish hearts of sinners, who therefore are said to crucify him afresh and put him to open shame.

Those that truly repent of sin look upon Christ as one whom they have pierced, who was pierced for their sins and is pierced by them; and this engages them to look unto him, as those that are deeply concerned for him. 

This is the effect of their looking to Christ; it makes them mourn.  This was particularly fulfilled in those to whom Peter preached Christ crucified, when they heard it those who had had a hand in piercing him were pricked to the heart, and cried out, What shall we do”?

It is fulfilled in all those who sorrow for sin after a godly sort; they look to Christ, and mourn for him, not so much for his sufferings as for their own sins that procured them.  Note, The genuine sorrows of a penitent soul flow from the believing sight of a pierced Saviour.

(Matthew Henry Commentary

Christ the Faithful Pastor Warning His Church

If we would overcome these evil tendencies of the flesh, we must obey the counsel of our compassionate Savior.  There is no guess work involved.  The Lord Jesus tell us exactly what must be done:  Remember…from whence thou art fallen ([Rev 2:5 NKJV] 5 "Remember therefore from where you have fallen; repent and do the first works, or else I will come to you quickly and remove your lampstand from its place--unless you repent.) Repent…and do the first works.  That which ye already have hold fast.  Tenaciously adhere to the truth of God, the Gospel of His free and sovereign grace in Christ.  Be watchful, and strengthen the things which remain ([Rev 3:2 NKJV] 2 "Be watchful, and strengthen the things which remain, that are ready to die, for I have not found your works perfect before God.)  Buy of me! ([Rev 3:18 NKJV] 18 "I counsel you to buy from Me gold refined in the fire, that you may be rich; and white garments, that you may be clothed, [that] the shame of your nakedness may not be revealed; and anoint your eyes with eye salve, that you may see.) Without money and without price, by faith alone, we must buy from Christ the gold of His grace and the white robe of His righteousness, as we did in the beginning, and anoint out eyes anew with the eye-salve of His gospel.

(Discovering Christ in Revelation by Don Fortner)