To every man and woman in the world
Everyone -- all of humanity
for all but writing this book for me
"All but" is an idiom, meaning achieving (literally or figuratively) most of the activity or state described. Eg (source):
Fundamentalism is a religious movement that seemed all but dead after
its heyday in the 1920s but that has shown rather amazing new strength
Now all but useless, these facilities go on draining the railroads in
property taxes and in wages for stationmasters and telegraphers.
The implication is that all of humanity effectively wrote the book, and the author only "channeled" humanity to write the words down.