Q. Who are the great multitude in white robes in Revelation 7:9, 14? This question is actually answered right in the passage. In Revelation 7:13, one of the elders approaches John and says, "Who are the ones arrayed in white robes?" It then tells us that this great multitude has the palms, and they're wearing white robes. And John says, "Sir, you live here, you know." So the elder says, "These are the ones who have come out of great tribulation, and washed their robes and made them white in the blood of the Lamb."
So the great multitude, we believe, is the group who is saved through the ministry of the 144,000. Now the 144,000 are 12 times 12,000. On Pentecost, God was missing one apostle. At the very beginning of Acts, there are only 11 apostles. Judas is eventually replaced, and then the apostles are filled with the Holy Spirit in the second chapter. Those 12 apostles reach a great multitude of 3,000 that were baptized.
Now this took place after the first coming of Christ. For the second coming of Christ, just before Jesus returns, 12 times 12,000 are going to baptizedand not just Jews, but the whole world. That's why there's more of them. This great multitude are converted through the influence of the 144,000. They are a massive harvest that comes just before the blessed hope of Jesus' return.
I have a book called "Who Will Sing the Song?" that explains this with a lot more evidence. Please call and order this book or go online!