Swedenborg was operating about a hundred years before the spiritualist movement got going- so he didn't have the technical language to talk about his mediumistic and occult carryings on. In this book he deals with aliens- including ones from outside our solar system. Sometimes the aliens are visiting him at home- travelling in globes that sound not unlike modern UFOs- and entering his consciouness and communicating with him mind to mind- and at other times he's travelling out of the body across vast tracts of space and seeing alien worlds for himself. He takes his Protestant Christianity with him, shares it with his contacts- and finds they have very similar beliefs. All his aliens are spiritually advanced, but technologically backward, with no knowledge of the sciences as practised on earth- and all look human, but with variations. He keeps running into spirits from the planet Mercury- who are as keen on interstellar travel as he is- and mischievous and inquisitive and not always truthful- and also bands of out-of-the-body Catholic missionaries who are trying to convert the aliens- but with little success. Swedenborg doesn't like the Catholic Church ("The new Babylon") and neither do the aliens.
I'm not here to mock. I think Swedenborg was a great man- and truthful. I think he really experienced the things he's telling us about. The incoherence of the narrative is a guarantee of its honesty. So is its oddity. This is a writer operating at the very edges of the sayable.