the meaning behind zack's death

When Zack died on that lonely hill in Midgar, he left one thing behind. A boy, his friend, whom he had carried across the globe to give a chance at a new life, it was this same boy whom he sacrificed himself for and in doing so provided this boy with a gift. His dreams, his honor, and his pride, all of the things that made him a SOLDIER, he gave to Cloud in the form of the buster sword. Beyond that, he gave Cloud a burden; one Cloud would bear for the rest of his life to be Zack's "living legacy". As Cloud limped away from Zack's cold, breathless body, a new story began.

It was through Zack's death that the life of the events of the game Final Fantasy VII started. With a lost boy whose memories and strength had all but left him long before. Cloud would have to fight for both Zack and himself. Cloud lost himself at some point in Hojo's lab as a weak, pale, cadet, and when Zack died, Cloud was reborn a became a hero. In his torn apart mind he could no longer differentiate himself from Zack. He believed that he was a first class SOLDIER and even forgot that a man named Zack Fair existed in the first place. Cloud was able to fight without inhibitions of his younger self's weakness to fight at the same level as Zack had been in life. Of course, the constant injections with Mako and Jenova Cells during his four years in captivity didn't hurt either.

It is highly unlikely that the game's ending would have been so pleasant if it hadn't been for Zack. His belief in Cloud, in the bond they shared gave the shy boy who wouldn't have even had the strength to hold his sword the confidence he needed to become more than he ever thought he could be. Through their bond Zack's strength became Cloud's which in turn enabled to triumph over the enemy of the world. In essence Zack's ending was just really just a new beginning, one where the old world, the experimentation, the mako pollution, the old Shinra, was all ripped away as the world was born anew. Cloud, who had lost everything in Nibelheim and in his battles against Sephiroth was given a reason to live and fight. Zack's death was a steep price to pay but in the world of Gaea it was well worth the result. Without Zack's death, Sephiroth would have undoubtedly succeeded in destroying the world. Why? Cloud wouldn't have the confidence to defeat Sephiroth which would only leave Zack. While Zack was good, he had reached his limit on that hill in Midgar, and even if he had lived, he would never have the ability to fight Sephiroth as an equal.

Is it possible the events would have remained the same without Zack? Yes, however it is unlikely, considering that Cloud was stuck poisoned and sick in Hojo's lab and that without Zack he may not escaped. Assuming he did, his super human strength alone wouldn't have been enough, because Cloud had been small, aloof, and filled with doubt about his own abilities. Cloud would have most certainly died on that cliff without Zack to protect him and take the brunt of Shinra's army. In the end, no matter how much we speculate on what would have happened to Cloud, the death of Zack as a hero began Cloud's life as a hero.

This fact is undeniable, and even Cloud says that Zack's death was just the beginning. In Advent Children Complete Denzel asks if the hill, now overgrown with flowers is a grave. Cloud replies that's it's not, it's where a hero's journey began. Cloud knows that he owes his life, and his livelihood to Zack and that without him, he wouldn't have been able to save the world.