Answer
Scripture promises that Christ will return to earth, yet the various passages predicting that event seem to indicate two separate returns. Revelation 1:7 describes a return in which every eye will see Him. First Thessalonians 4 describes a return in which not everyone will see Christ.
As John introduces the book of Revelation, he alludes to Zechariah 12:10 and asserts that Jesus Christ is coming with the clouds and that “every eye will see Him” (Revelation 1:7). Roughly five centuries earlier, Daniel recorded a similar scene in which he observes that a Son of Man will be coming with the clouds of heaven (Daniel 7:13) to begin an eternal kingdom over the earth (Daniel 7:14). Paul describes the Lord descending from heaven with a shout, the dead in Christ rising from the dead, and then those who are in Christ and still alive being caught up in the clouds to meet the Lord in the air (1 Thessalonians 4:17).
John, Daniel, and Paul all mention clouds associated with the coming of the Lord, but, despite the similar terminology, there are differences in the prophecies. Daniel says that Jesus will immediately begin His kingdom upon His return. In the coming that Paul prophesies, Jesus doesn’t actually come to the earth; rather, those who are caught up to Him remain in heaven with Him (1 Thessalonians 4:13), after which Paul describes the day of the Lord taking place (1 Thessalonians 5:2ff). This does not seem to be the coming of Jesus when every eye will see Him; instead, this is more like what Jesus said in John 14:2, when He said He would go to prepare a place for His followers, come again, and receive them to Himself so that where He is they would be also.
In John 14:2, Jesus describes His going from earth to heaven (going to prepare a place), then coming from heaven but not all the way to earth (receiving them to Himself), then remaining in heaven (where He is they would be also) for a time. Similarly, Paul describes the event of saints joining Jesus in 1 Thessalonians 4:13–17 and in 1 Corinthians 15:51–52. In the latter passage, Paul describes believers changing and being with Christ in the “twinkling of an eye”—a sudden event that is perhaps so quick as to be visually imperceptible. This does not seem to describe something that every eye will see—something so vivid and broad that everyone on earth will witness at the same time.
In Revelation 19:11–14, John describes Jesus coming to earth with armies of saints and then reigning on earth with them (Revelation 20:4). As those saints are already physically with Christ, the event that brings them together has already happened. The chronology indicates that the event Jesus and Paul describe involving the “catching up” of believers to Jesus will have already happened before the return of Christ in Revelation 19—also referred to in Revelation 1:7—Jesus’ coming in the clouds. The first of these two events is often referred to as the rapture, because of the Latin word for “caught up” (in 1 Thessalonians 4:17). The second of these events is typically referenced simply as Jesus’ second coming, because it is the second time recorded that He actually comes to the earth (unlike the rapture, in which He only comes in the clouds to meet His believers in the air).
At the rapture, only believers will see Jesus. At the second coming, every eye will see Him—the whole world will behold Him. It is this second event to which John refers in Revelation 1:7.