Seek the LORD while He may be found., page-25

"So, what is this process they have washed their robes and made them white in the blood of the Lamb. ?"

Your wording is questionable here.
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All translations I have read agree that the reason these ''come out'' alive is because they have accepted the ransom by praising Jehovah and Jesus for providing it and learning to bring their lives into harmony with God's will. It is because of this they are accepted as righteous.
You have only supplied the book of Wotsup to support your idea.

Revelation7: ¹⁴ So right away I said to him: “My lord, you are the one who knows.” And he said to me: “These are the ones who come out of the great tribulation, and they have washed their robes and made them white in the blood of the Lamb. ¹⁵ That is why they are before the throne of God, and they are rendering him sacred service day and night in his temple; and the One seated on the throne will spread his tent over them.