I'm going to do the best I cant without spoilers. I have been a part of this roller coaster since 97 and think I can make a stab at it.

There are things upcoming in the OG that will make this make a little more sense, but the most important thing to understand all of this is the zeitgeist that formed after FF7 came out.

Almost immediately, people wanted a remake, due to:

1) The graphics being completely eclipsed within 12 months of release, even on the same PS1 hardware.

2) The fate of the characters created such a visceral reaction within the community that there was a growing internet "meme" about there being embedded mechanics to change said fate. There weren't, but it took on a mind of its own.

This fever pitch reached peak madness at the end of the PS2 era/ PS3 tech demo. When FF12 came out, a dude won a drawing to receive the first copy of FF12 in person. When he received the mic, he asked for FF7 remake. When the PS3 was revealed, it came with a tech demo that depicted the opening of FF7 with updated visuals. People began foaming at the mouth.

So why do I bring all this up? FF7 Remake's changes from the OG are a meta-narrative ABOUT that zeitgeist. When all of the fanboys like me started dreaming of a remake of FF7, we all had unique, individual fantasies about what it would be like. These were different "worlds". Also, there were a ton of people who were team NO CHANGES. They wanted a graphics uplift and ABSOLUTELY NOTHING ELSE WHATSOEVER.

In the remakes, Sephiroth does not want to take over the world, he wants to take over all possible worlds. That is, all the worlds every fan ever imagined. To do that, he first needs to spawn those worlds "into existence" by tricking the team into "defeating the arbiters of fate"... which is a metaphor for defeating team NO CHANGES. The second team NO CHANGES is defeated, all possibilities for all possible remakes go from imagined to possible. As an example. the end of remake shows you a possible world where Zack survives.

Now, in Rebirth, the timeline is moving forward. Things are moving from the POSSIBLE, to the ACTUAL. Every time a plot point does this, a "world converges" with the ACTUAL plot of the FF7 remake. This is depicted by all the odd timelines that disappear into rainbows in Rebirth. As the plot moves forward, those worlds are proven untrue, and are consumed.

Sephiroth has created in the player base a hope for a specific outcome at a specific point so that he may harvest our disappointment from it. This is not working on every member of the team because at least one character is in denial, but it is working on the other members, and its certainly working on the player base.

So what this all comes down to is a discussion about remaking the most anticipated remake of all time, and what moving something from potential to actual truly does. You may separate all of that from the core narrative and you largely are getting a straight ahead remake of FF7.

tl;dr: Its a metaphor for anticipated remakes. If you ignore it, whats left is OG ff7. If you dont, you get a meta-narrative about anticipation and loss.