Hello,

You asked,
And can you say me which books should I read to know more about eternal progress and life in spheres? I've heard about Letters of Pierre Monnier but I do not know where I can get it?

I don't know about Pierre Monnier. But we have a great library of descriptions of the afterlife from direct-voice mediums and mental mediums. Read about what those in the afterlife say or listen to the recordings. They're the authorities, since they live there.

Get Crookall's The Supreme Adventure. In it, he has compiled the descriptions from those in the afterlife provided by dozens of mediums.

Listen to the recordings on my Web site, adcguides.com or at leslieflint.com. Listen to the recordings coming from David Thompson today at http://www.victorzammit.com/audio/index.html . You might also read Victor Zammit's book. He has it free online at http://victorzammit.com/book/4thedition/index.html and you can purchase the published version.

There's so much available now about the afterlife that you should go directly to the sources themselves before going to the secondary sources. Once you've exhausted all the direct testimonies from those in the afterlife, then perhaps go to the secondary sources. But you probably won't want to or need to.

Love and peace, Craig