The Seven Seals
Revelation 7 mentions two groups, the 144,000 and the great multitude. Who are these two? Are they the same? The first step is to notice that the 144,000 answer the cry of the wicked under the 6th seal, "Who shall be able to stand?" Next, notice that the phrase "white robes" (λευκαι, Strong #3022; στολαι, Strong #4749) only occurs in all of Revelation in the 5th seal and in the description of the great multitude and nowhere else!
Notice how Matthew 24 reinforces the structure enclosing the 5th and 6th seals and the 144,000 and the great multitude. It mentions a great tribulation as well as signs in the sun, moon, and stars occurring just before the Second Coming.