John is not talking to Israel in Revelation 1:5-6, he was talking to those who were in churches consistent of Jew and Gentile believers in the ancient Roman province of Asia. That Roman province doesn't even exist anymore, so how could he have been writing to future churches? You couldn't possibly be more off base about this if you tried.
Look at the tense being used in the verse. It's present tense. Jesus "HAS MADE" them kings and priests" as of the time John wrote the book.
As for what you said about Rev 1:1, did you not read this verse...
Revelation 1:19 Write, therefore, what you have seen, what is now and what will take place later.