Way Station by Clifford D. Simak
The premise of this story is that there is a community of worlds and intelligent species in part of our galaxy. As time goes by and the community discovers new inhabited worlds around the periphery of the area of the galaxy they're familiar with, the size of the community grows. The worlds in this community are linked by a network of teleportation stations. Teleportation is only reliable over a limited interstellar distance, so a person traveling from A to D must pass through relay stations B and C. Apparently, the travel from station to station is more or less instantaneous. At each relay station, the person is recreated from chemicals stored at the station. Then when the person is sent to the next station, it's really just the description of him that's sent. The recreation of the person at the intermediary relay stations is sent back into the chemical storage tanks. In between arriving at a relay station and being sent off to the next station, there is often a waiting period during which the traveler may spend time with the person running the relay station.
Shortly after the US Civil War, this interstellar community has found it would be convenient to have a relay station on Earth. They find a Civil War veteran, Enoch, living in an obscure corner of Wisconsin who meets some (never explained) criteria to run the station. He is the only person on Earth who will know about it. His cabin is converted inside to have all the hi-tech necessities, but the house looks the same on the outside. Some aspect of the station prevents Enoch from aging when he is within the building. He only ages for the limited amount of time he spends outside. It's now about 100 years later. Enoch looks to be in his 30s. He's let his land go back to a mostly wild state.
Enoch is friends with the alien who recruited him for the job and has been friends with some of the regular travelers using his station. He has used some of his time over the years to learn about some of the cultures from other planets.
His main connection to the rest of Earth is through the mail. He subscribes to a number of newspapers and science magazines (partly for his own benefit, partly for the aliens). The newspapers are full of gloomy reports making another world war seem probable. He'd like to do something to help, but there's not much he can do. He'd like to tell the world about the community of intelligent species, but he's not allowed to. Besides, who'd believe him and what would they do if they did believe him?
He talks with the mailman when the mail comes. Enoch and the mailman get along, but he doesn’t have much to do with other humans. This and the oddity that older people know he’s been around such a long time without getting old has led to the locals having suspicions about him.
For some reason, a CIA agent took interest in stories of a man who doesn't seem to age and seems to be the same person who served in the Civil War. Eventually, this leads to an organized surveillance of Enoch and his land.
And meanwhile, there are problems brewing in the interstellar community. They have some gizmo that is used by what is sort of a spiritual leader that helps keeps the community working together harmoniously. They've had an inferior spiritual leader for a while (apparently, they've had trouble finding the right person out of all their zillions.) Now the gizmo is missing. As a result, there's more friction in the community.
Much of the technology in the book is implausible, but at least Simak doesn't spend time explaining how it's supposed to work. The spiritual gizmo pushes the implausibility further. It because part of a fairy-tale-like subplot.
Here and there Simak will write lyrically for a while, but then goes back to storytelling. To me, Way Station works more as a story of Enoch - a man separated from his own people by the passage of time, by his secret work, by his isolated location, etc. Also, about his relationship with the aliens and his loneliness for other humans. It's also interesting as a concept of interstellar relay stations. On the other hand, the story of international and interstellar conflict needing to be resolved by the right person wielding the "magic wand" of peace was too simplistic for me.
There are a number of glimpses at aspects of possible aliens, but these are of limited depth and extent. They add to the story, but are only a small part of the book.