Apocalipse 1:7

Behold he cometh with the clouds; and every eye shall see him, and they that pierced him; and all the tribes of the earth shall mourn over him. Even so. Amen.

This is the topic-sentence of Revelation, a great deal of which relates to the final judgment, an event mentioned at least seven times in the prophecy; and these are not seven different kinds or occasions of judgment, there being only one judgment day, the final and awesome event that shall conclude the dispensation of grace, see the resurrection of the dead and the assignment of every man's destiny, and bring the redeemed into their eternal habitations. It will occur at the Second Advent of Jesus Christ our Lord.

Behold he cometh with the clouds ... These words apply to the Second Advent, as in Matthew 24:30; Mark 14:62; Acts 1:9-11; and Mark 13:24.

Every eye shall see him, and they that pierced him ... There is no connection between this and the passage in Zechariah, except that the terminology is similar, the great difference being that in the Old Testament their looking upon the one who was pierced, and mourning, was grief for the pierced one, not grief for themselves, as is clearly indicated here and in Matthew 24:30, which words John evidently had in mind when this was written. To understand exactly the object of the mourning here, one should read Revelation 6:15-17. See Zechariah 12:10-13:1.

All the tribes of the earth shall mourn over him ... This clause, along with the preceding "'every eye shall see him" indicates the final judgment, that being the only occasion when all the tribes of earth and every eye (that is, every man) shall behold the Christ.

And they that pierced him ... Even the generation that crucified Christ will not be exempt from confronting him in the final judgment. The mourning here mentioned will be due to the startling realization on the part of the wicked that the whole course of their lives has been wrong. The atheist will suddenly know that God is a reality. The proud, the arrogant, the thoughtless, the sensualist, the materialist, and all who have lived as if there were no God shall be summoned to a judgment which they have never allowed as even possible. The mourning of people in that circumstance will surpass any possible description of it. And the mourning will not be "over Christ" in the sense of their grieving for what was done nearly two thousand years ago TO HIM (how could people even imagine such an interpretation?). No, their grief will be for themselves. The Second Advent will be bad news indeed to the vast majority of mankind.