The following content was originally written as a response to a Reddit post.
The Genesis 1 account is a story. That is how it would have been experienced. A parent or teacher or elder would recount the story of the creation of the world by God to a listening audience. It would be intended as a moral Truth story. The storyteller would expect the audience to believe and be guided by the story, to find in it comfort and instruction. That would be the purpose of telling the story and faithfully handing it down from one generation to the next. Such a story is meant to be taken as Truth and therefore not freely modified as one sees fit, but rather related in full and with precision.
We call a true story a narrative and the three modifiers tell us what kind of story. First of all, it is clearly a poetic story. That is different than being a poem. In this case poetic means that the story employs metaphor and structure. It utilizes inclusiowhich is to wrap a concept in an envelop structure. It also utilizes chiastic structure which is the organization of concepts in the A-B-B-A repetition. The repetition and structure of Genesis 1 is quite obvious, even though the text is written as a narrative rather than as a poem.
To say that it is historical is to state that the events of the story represent true history. That is, God actually performed each of the creative miracles described at some point in the past. It also implies the general sequence of events is meaningful. There really was a time when these things happened.
To say that it is an epic telling is to recognize that the sweep and scope of the story is both very grand and very profound and that the author employed elements of epic story telling. One of the elements is that of epic regression which we see in Genesis 1:14-19 which narrates the Fourth Day and harkens back to "let there be light" of Day 1 and the "heavens" of Day 2. The telling of the events of Day 4 in which the lights begin to mark days and years and serve as signs for seasons is couched in terms that relate back to the original appearance of light, the demarkation Day and Night, and the formation of the Heavens. Without recognizing the employment of epic regression one might mistakenly think that all the events are crammed into Day 4. We also see parallelism between seas and land of Day 3 and the filling of the seas and land on Days 5 and 6. The parallelism does not negate the sequence of events but points to the purpose of the sequence. Another element of the epic is that the narrative relates the events in sweeping, encompassing terms in order to avoid a massive list of specific details. This means that we must interpret the events as generalizations. Most birds were created on Day 5, most plants on Day 3, etc. Exceptions here or there would not be the point. It is an epic. If an epic were relating the progress of a war it would gloss over many battles and merely hit the highlights, the true turning points of the war, not every maneuver. That is what we have in Genesis 1 as an epic.
We could add to all of this that Genesis 1 is a polemic. A polemic is an attack or a defense. The author is basically saying, "Let me tell you how it really happened." This narrative is put up against other competing creation narratives and is being put forth to set the record straight. It argues against competing ideas of polytheistic creation stories. The six days of creation may be set against the six gods of Sumerian creation mythology. The reason why some parallels are seen between Sumerian creation stories and Biblical creation stories is likely because the Biblical accounts are written to counter the Sumerian accounts. This points to these stories being very ancient, likely authored about 2000 BC or so.
So there you have it. Genesis 1:1 to 2:4 is summarized in the colophon captured in Genesis 2:4 and was written about 2000 BC, likely on a clay tablet, in the epic, historical, poetic narrative literary genre to serve as a polemic against false creation mythologies and in being revealed by God, the True Creator, also conveys key elements of the actual history of Earth.
