The question that was asked is: what you understood by the tribulation that is mentioned in Revelation 7. Let's look at this verses and see if you understand where it is lacking from your outlook
9: After this I beheld, and, lo, a great multitude, which no man could number, of all nations, and kindreds, and people, and tongues, stood before the throne, and before the Lamb, clothed with white robes, and palms in their hands; - Look at what is written and where these people are. You do not see them coming out of the earth. These are the people who are already there with the Lord. Here you not referring to Israel but to the multitudes that are already taken to be with the Lord. You do not see this happening on earth.
10: And cried with a loud voice, saying, Salvation to our God which sitteth upon the throne, and unto the Lamb. - The throne of God, where do you believe it is? It is in heaven. That would mean these people are with the Lord. they 'stood' before the throne in verse 9. They were not quickened, they were not raised. They were already there. They were taken to be with the Lord.
Now going to the later verses:
13: And one of the elders answered, saying unto me, What are these which are arrayed in white robes? and whence came they? - This is a question to ponder upon at many levels. He knew the answer, he knew Ap. John. But he still asked. Why would he do that? If he did not, how will we know?
14: And I said unto him, Sir, thou knowest. And he said to me, These are they which came out of great tribulation, and have washed their robes, and made them white in the blood of the Lamb. - Did Ap. John not know? Of course, he did, he was having these visions and he was in the spirit. The spirit searches the deeper things of God. It reveals things. Why did he not then answer? Observe that revelation is not about what Ap. John says but what he has seen and heard. He wanted to testify to what was seen and heard. And that is why it is more credible to hear from the one above. Just like the thundering when Christ was baptised and also in another occasion in the gospel of John. Then what is the understanding here? What tribulation are you talking about? For a clearer understanding, it would be better to meditate upon the hope that one has in the Lord. Believers are never meant to endure the wrath of God. This can be understood from the NT.
15: Therefore are they before the throne of God, and serve him day and night in his temple: and he that sitteth on the throne shall dwell among them. - Now looking at this, why does the writer of Hebrew stress on the throne of grace which we approach boldly? Do we believe that every Christian who believes is washed in the blood or not? If you do, then does those believers in the 'tribulation' differ from us who are also allowed to approach the throne of God at any time of our lives? Or are we and they, the same? Why do Ap. Paul, Peter, John and the other stress on the hope that we have in the Lord?
Think and meditate about this, then you will see what I am talking about. I finally stop here.