Revelation 1:1-8 Greetings And Doxology

revelation” / “apocalypse” means “unveiling” or “disclosure” – what is being disclosed?  What is the double blessing that begins this book? Why 7 churches?  What is the significance of “from Him who is, and who was, and who is to come”?  (see also v.8 and 4:8)  What is “the 7 spirits” / “seven-fold Spirit”?  (see Isaiah 11:2)   How is Jesus described in these verses?