Rv 1:1-8 is a summary and conclusion of all the chapters of Revelation. Rv 1:7 is part of that summary.
Clouds are capable of hiding things from view. The fact that Jesus returns with the clouds means that he is coming in spirit. In Acts 1:9-11, Jesus’ disciples were staring into the sky after Jesus’ ascension, and a cloud hid Jesus from their sight. Some angels told the disciples, “This same Jesus who has been taken up from you into heaven will come back in the same way you saw him go into heaven,” (Acts 1:11b). Matthew 24:31 says that Jesus will return with his angels, while Mt 24:27 says the coming of the son of man will be like lightning. Luke 17:22-24 says, “The days are coming when you will desire to see one of the days of the son of man, and you will not see it. For just like the lightning flashes and lights up the sky from one side to the other, so will the son of man be in his day.” Jesus also says in Jn 16:10, “Concerning righteousness, because I am going to the Father and you will see me no longer.” Apostle John saw the spirit of Jesus in Rv 1. The one who comes with the clouds is referring to the angel in Rv 10—the angel who comes in the name of the Lord.
In Mt 23:39 Jesus said, “You will not see me from now until you say, ‘Blessed is the one who comes in the name of the Lord!’” The one who comes in the name of the Lord is the Advocate—the spirit of truth mentioned in Jn 14:26—which dwells within a person (Jn 14:17). The one in whom the Advocate—the one who comes in the name of the Lord—dwells also becomes “the one who comes in the name of the Lord.” Seeing the person in whom the spirit of the Advocate dwells is the same as seeing the spirit of the Advocate, who is the one who comes in the name of the Lord. If Mt 17:10-13 and Mt 11:14 are taken together, seeing John the Baptist, who came in the name of Elijah, was the same as seeing Elijah. According to Jn 5:43, Jn 14:8-11, and Jn 12:44-46, Jesus came in the name of the Father, and the Father dwelled in Jesus. Seeing Jesus, therefore, was the same as seeing the Father, and believing in Jesus was the same as believing in the Father. Similarly, God, Jesus, and heaven come down to the one who overcomes (Rv 3:12), and the one who overcomes sits on Jesus’ throne with him (Rv 3:21) at the time of the second coming. Hence, saying that Jesus comes with the clouds means that he is coming in the spirit. It is just like a cloud that hides things from people’s sight.
The fact that every eye will see him means, as discussed above, that people will see the person with whom the spirit of the Advocate has united. Seeing that person is the same as seeing the Lord. It is true that the spirits of those who pierced Jesus at the time of the first coming will see the spirit of Jesus when he returns at the time of the second coming, but the eyes of those who pierced Jesus (Rv 1:7) do not refer to those physically dead people. Because God was one with Jesus at the time of the first coming, those who pierced Jesus pierced God as well (Jn 15:23). In the same way, those who pierce the witnesses standing before the Lord in Rv 11 pierce Jesus at the time of the second coming.
The earth in Rv 1:7 is the same as the earth in Rv 13:8-10. It symbolizes God’s chosen people (the sun, moon, and stars mentioned in Gn 37:9-11) who are destroyed and return to being mere flesh when they fall from heaven. The destruction of the chosen people occurred in Adam’s time, Noah’s time, and Jesus’ first coming. What does it mean for all the tribes on the earth to mourn because of him? Just like the song of Moses in Dt 32 and the Lamentations of Jeremiah, it is a sound of mourn of the capture and destruction of God’s chosen people by the figurative nation of Babylon as a sign of the second coming. Although the two witnesses before the Lord put on sackcloth and work to help these formerly chosen people to repent, can the people understand if their spirits are dead? Anyone who is not harvested to receive salvation at the figurative Mt. Zion (Rv 14) will mourn. They are not mourning the death of the two witnesses; they are mourning because their dead spirits of those who were captured by the gentiles after falling from heaven due to their betrayer failed to believe in the one who comes in the name of the Lord.