Zechariah 12:10b goes on to say, "They will wail over Him with wailing as for an only son and cry bitterly over Him with bitter crying as for a firstborn son." An only son is most dear to his parents, and a firstborn son has honor among the many sons. Repentant Israel will wail over Christ as the only Son of God and will cry bitterly over Him as the firstborn Son of God.
In the New Testament Christ is revealed first as the only begotten Son of God and then as the firstborn Son of God. John 1:18 says that the only begotten Son, who is in the bosom of the Father, has declared Him. John 3:16 tells us that God so loved the world that He gave His only begotten Son. Through His death and resurrection, the only begotten Son became the firstborn Son (Rom. 8:29; Heb. 1:6a). According to the New Testament, Christ's being the only begotten Son is for us to be redeemed and to receive eternal life. Christ's becoming the firstborn Son through death and resurrection is for us to become sons of God as heirs to inherit all the riches of what God is, that is, to receive, participate in, and enjoy all the riches of the Triune God. In their repentance Israel will recognize Christ both as the only begotten Son of God and as the firstborn Son of God. They will realize that as the only begotten Son Christ has redeemed them and has brought them eternal life and that as the firstborn Son He has made them heirs to inherit the riches of the Triune God as their enjoyment.
In that day there will be great wailing in Jerusalem. The land will wail, every family apart: the family of David and their wives apart; the family of Nathan and their wives apart; the family of Levi and their wives apart; the family of the Shimeites and their wives apart; all the families, the whole household of Israel, that remain (Zech. 12:11-14). Here we have three kinds of families: the royal family of David, the family of the priesthood (Nathan and Levi), and the family of an evil man (Shimei, who cursed David). Zechariah uses these families as illustrations. All those who look upon Christ, the pierced One, with a repentant spirit, will wail over Him.