What is the great tribulation?

Revelation 7:14 (ESV)

14 I said to him, “Sir, you know.” And he said to me, “These are the ones coming out of the great tribulation. They have washed their robes and made them white in the blood of the Lamb.

Popular understanding has the term describe a period of persecution just before Christ’s return. Different brands of Dispensationalism will place the Great Tribulation before or after an expected Rapture. The text itself, however, contradicts this understanding and requires a very different explanation. Consider the following observations:

The elder says, These are the ones coming out of the great tribulation. He is referring to the innumerable crowd of Revelation 7:9, people coming from every nation and all tribes, peoples and languages. In the period before Christ’s return some nations, tribes, and languages have disappeared. That indicates that the crowd John sees is not limited to those who live in the time surrounding Christ’s return. His reference is to saints of all ages touched by the salvation of God.
The elder describes ongoing action when he says that these are…coming out of the great tribulation. The action was happening before John’s eyes and would continue to happen through the ages.
The context of this vision is important. The Lord had interrupted the opening of the seventh seal because of the desperate question asked in Revelation 6:17: given the horrors of the wrath of God, who can stand? The horrors of God’s wrath had been expressed in the war, death, famine, and pestilence of the earlier seals and the martyring of the saints in the fifth seal and now culminated in the terrors of the day of God’s wrath in Revelation 6:12–17. Revelation 7:9 answered the question of who can stand with the vision of the great multitude, those who have come out of the great tribulation. In context, the great tribulation can only refer to what it is like to be on the receiving end of God’s righteous judgments.
The term great tribulation does not contrast with, say, minor tribulations. Rather, the term gives expression to the horror of God’s wrath—and experiencing that wrath is always horrible, great in a very negative sense.

We need to conclude that the phrase great tribulation in this passage refers to the ordeals that occur when the seals are opened. These ordeals do not pass by the servants of our God (Revelation 7:3).