im asserting the scroll has little to nothing to do with unsealing the death god as some believe and i state my case in the dedicated thread to orochimaru's super secret scroll.
what the scroll is is a huge clue behind the uchiha massacre. they take the scroll to the uchiha shrine to specifically summon the hokages in the presence of the stone tablet. there is a potent mystique of " knows everything" in the scroll followed by going to "where all the secrets lie". since the "secrets lie" within the uchiha's temple then the uchiha must have known the secret. a serious secret of the highest magnitude heyond the 9 tails, of a magnitude large enough to drive them to the entire clan rebelling and so severe that if sarutobi was privy to the secret he would allow the entire clan to die! it's a secret that tobi and madara also wanted to prevent which is why tobi shows up in secret and has motives to kill uchiha as well but doesn't reveal the true motives or secret to itachi. the secret is likely a timed event like a rare lunar cycle or special ultra jutsu.
it's a secret into what's behind the destiny of the bloodlines and why they fight. the senju alligned hokages at odds with the uchiha where one sidecwants something to happen and other wishes to prevent all at highest costs. madara betrayed the secret and became his own end and the uchiha betray madara by sticking to the secret. rest assured, that the uchiha were wiped out due to whatever that scroll is related to and is a key piece to the what the uchiha feel as their destiny. notice that the only uchiha to be edo tensei were madara and itachi. any other uchiha would be privy to the secret and great care was taken to secure all the remains and out if reach of techniques like edo tensei.