If Tifa and Aerith fought...

[Timerk]

Isn't that basically the same thing?

Yes, Aeris was the only one in the party who could summon Holy, that is why she got stabbed.

I'm not disagreeing that she was the only one who could do it then. What I am disagreeing with is the concept that it was somehow limited to just being cast by the cetra, instead of anyone with the knowledge and will to cast it.

It is unclear, but I believe to summon Holy, you would have to develop a relationship with the planet that was the same as the relationship the Cetra had with the planet. That means a non-Cetra would have to be very much devoted to the planet, and love the planet, in order to summon Holy. I don't think it would be possible for anyone in the party to be that way (except maybe Red XIII, but not at the time of the game, though).

If Sephiroth was really worried about the White Materia after he killed her, he just would have had Cloud bring it to him along with the Black Materia.

Well, it kind of fell into the water and sank in the ancient city, so that's kind of not an option.

The Black Materia was pretty tucked away too, and Sephi still managed to get it. I would say that if he really thought the White Materia would stop him, than he would have found a way to get it and destroy it.

Sephi had a very low opinion of people who did not come from the Cetra, so I think that even if someone could summon Holy other than Aeris, he wouldn't think it would be Cloud or the party. He prolly thought they were too stupid to figure out how to use it.

Also, in the ending, Marlene says she can sense Aeris when Holy arrives, which I took to as it was Aeris personal connection with the planet that allowed Holy to be summoned.

Well, Aerith's will was the one that called forth Holy, same as Sephy's called forth Meteor. I don't see why that means her connection was a necessity for it to be cast, though.

Maybe, but I don't think they would have put that line in if it wasn't important. If nothing else, it shows Aeris spirit was in Holy, which would seem to make Holy more than a generic spell anyone could case.

I can't imagine Cid summoning Holy.

He doesn't seem the type to cast it either, especially based on his speech before the crater, but I do not believe it's impossible for him to cast it, since I don't think the cetra are complete smegheads who would be so foolish as to put an 'us only' limiter on the counter device to a horrible destructive force that could inflict massive damage on the planet they tended and venerated.

Ah, but could the Cetra have been so overconfident that they never thought they would be wiped out? Or perhaps they did not see the world becoming a place so hostile to the planet? Or maybe the felt that once they were gone, anyone left to summon Meteor did not deserve to be saved?

Regardless, I believe it requires a very strong spirtuality to summon Holy, and everyone in the party didn't have that.