The vastness of the Lord’s heaven also follows from the fact that all the planets we can see in our solar system are earths, and especially that there are untold more in the universe, all inhabited, as discussed in a special booklet entitled Other Planets, from which I should like to cite the following.
It is common knowledge in the other life that there are many planets with people on them and therefore angels and spirits from them, since anyone who wants to talk with spirits from other planets because of a love of the truth and a desire to be useful is allowed to do so to be convinced of the plurality of worlds, to learn that the human race is not just from one earth but from countless planets.
I have talked about this on occasion with spirits from our earth, noting that intellectually gifted people could know, on the basis of much that is familiar to them, that there are many earths with people on them. That is, they could come to the rational conclusion that masses as big as the planets, some of which are larger than our earth, are not empty lumps created only to meander around the sun and radiate their feeble light for just one planet, but that their function must be more worthwhile than this.
People who believe (as they should) that the Divine created the universe for the sole purpose of the emergence of the human race and a heaven from it (for the human race is the seedbed of heaven) cannot help but believe that there are people wherever there is a planet.
It is abundantly clear that the planets visible to our eyes, the ones in our solar system, are earths, because they are material bodies, since they reflect the sun’s light; and when we look at them through a telescope they do not look like ruddy, fiery stars but like earths with blurry bands of color. There is also the fact that they are borne around the sun, through the stations of the Zodiac, just like our earth, which must cause years and the seasons of the year called spring, summer, fall, and winter. Similarly, they rotate on their axes like our earth, which makes days and the times of day called morning, noon, evening, and night. Not only that, some of them have moons called satellites, which have their own periodic orbits around their sphere the way the moon orbits our earth. The planet Saturn, which is very far from the sun, has also a huge luminous belt that gives a great deal of light to that planet, even though it is reflected light. How could anyone who knows all this and thinks rationally say that these are empty bodies?
Then too, I have talked with spirits about the fact that people could realize that there is more than one earth in the universe from the fact that the starry heaven is so immense. There are so incomprehensibly many stars in it, each one a sun in its own place and its own system, like our sun, of different magnitudes. If people think this through carefully, they will come to the conclusion that this whole vast universe cannot be anything but a means to an end, which is the goal of creation, a heavenly kingdom in which the Divine can dwell with angels and with us. The visible universe, the heaven spangled with so incomprehensibly many stars that are all suns, is in fact simply a means for the production of planets with people on them who can make up a heavenly kingdom.
Given all this, rational people cannot help thinking that such a vast means toward such an end did not come into being for the sake of a human race on one earth. What would that be for a divine being, an infinite being, for whom thousands or tens of thousands of planets, all fully inhabited, would be so slight as to be practically nothing? There are spirits whose special passion is to learn at first hand, because this is the only kind of knowledge that gives them any pleasure.
These spirits are therefore allowed to travel around and even to leave this solar system and visit others, to gather firsthand knowledge there. They have told me that there are inhabited planets not only in our solar system but also outside it in the starry sky—a vast number of them. These spirits are from the planet Mercury.
By a preliminary calculation, if there were a million planets in the universe with three hundred million people on each one, and two hundred generations over six thousand years, and if each person or spirit were allotted three cubic cubits, and if all these people or spirits were gathered into one place, they would not even fill the volume of our earth, hardly more than a satellite of one of the planets. This would be such a small space in the universe as to be barely visible, since we can scarcely see those satellites with the naked eye. What would this be for the Creator of the universe, for whom it would not be enough if the whole universe were filled? For the Creator is infinite. I have talked about this with angels, who have told me that they have much the same idea about how small the number of the human race is in comparison to the infinity of the Creator. However, they do not think in terms of space but of states, and to their minds, no matter how many tens of thousands of planets you could conceive of, it would still be simply nothing to the Lord.
Information on the planets in the universe, their inhabitants, and the spirits and angels who come from them may be found in the booklet mentioned earlier. What you will find there has been revealed and shown to me to let people know that the Lord’s heaven is vast and that it is all from the human race, and also that our Lord is recognized everywhere as the God of heaven and earth.
from Heaven and Hell, Section 417