In the book Esoteric Physiology, Klocek describes how he understood the process by which the human being came about. I found that part useful to understand the astral body (the etheric body is something else, not touched here). In summary, when the human being was ideated through the cooperation of various other beings of the hierarchies, a number of contributions were made to that creation, coming from different levels of the hierarchy of beings. One of those contributions was the potential to form an inner image, out of an original experience. So the new being (the human being) was equipped with the ability to experience an Imagination created by a higher being (nothing else can be content of experience) and, for the first time, form an inner image of it.
From there, the subsequent step in the ideation of the human being was to say, ok, now that it can reflect the whole Cosmos in this way, and experience it as inner images, let’s make it able to experience a small part of those images as separate from the imaginations of the Cosmos, and let's enable it to hold on to that part. So the human being in the making was enabled to go from the experience of being one with all Imaginations, reflected as inner images, to the experience of holding on to a small subset of these images and experiencing them as separate from their creator. This means that these were now beings with their own consciousness, because they would consider this subset of imaginations and see that its source, what created it, was different from them, and they - the human beings - were different from it. In other words, at this stage the human beings are one and identified with the whole Cosmos, experienced as inner reflections, but there is a subset of the reflective images that they can see as created by something that is other than them. So they have the experience of otherness, of two, and they cling to that experience.
That subset of inner pictures that the human being keeps separate and experiences as created by someone else, is a kind of bug introduced in the Cosmos. Before that, all was fluid and one, but now, there’s this little piece of “something else” that is part of the Whole, but is perceived as estranged from the Whole of creation. In a sense it’s an anomalous force within the Whole, that encloses the potential for degeneration, because it lives off of the same Ideas as anything else, that it reflects, but it internally feels separate. This disruption of unity, this bug that cuts the smoothness and continuity of cosmic Ideation, forms a “kind of funny little world”, in Klocek’s words, and this funny little world, that’s slipped out of instant recognition of the one origin, is the human soul, or astral body. It is also the space in which human personality would develop.