For reasons unknown, even to himself, Angel stole the Scrolls of Aberjian whilst in Wolfram & Hart and gave it to Wesley to translate. Wesley discovered in To Shanshu in L.A that the scrolls contained a prophecy about a vampire with a soul who would be restored to a human, after fulfilling his destiny.

The Shanshu prophecy tells that the vampires will play a major role in the Apocalypse. Wesley realises that “Shanshu” means both to live and to die - so the vampire will become human and, as all mortals, eventually die. The trials the vampire would have to endure are unclear, but they would clearly be hard and numerous. No indication of time was given to the prophecy, but it filled Angel with a new hope that he would be redeemed.

Wesley: “Ah, the vampire with a soul, once he fulfills his destiny, will Shanshu. Become human. - It’s his reward.”
Cordy: “Wow. Angel a human.”
Angel: “That’ll be nice.”

This hope remained with Angel until the fifith season, when he began to doubt himself. Having taken over the L.A. branch of Wolfram & Hart, another vampire with a soul suddenly comes on the scene - his old nemesis, Spike. Spike had fought to regain his soul and had died saving the world, making Angel jealous on a basic level, and deeper, feeling the prophecy may in fact regard Spike. Spike was first told about the prophecy in Hellbound. Angel acted disinterested in the prophecy, but it was revealed that it would be the vampire who drinks from the Cup of Perpetual Torment that will become human. After a race to the cup, and a huge fight, Angel was defeated by Spike, who drank from the cup, only to discover that the story was a hoax.

Angel began to lose his way, but was finally put back on track by Cordelia, seemingly ressurected, who gave him a final vision, showing him the Circle of the Black Thorn, agents of the Senior Partners. Deciding to perform what would most likely be a suicide mission, Angel and his team assassinated each member of the Circle, thereby delaying the Apocalypse for an untold amount of time. In order to learn of the identities of the Circle members however, Angel had to infiltrate the group. To prove his loyalty, Angel was forced to sign his name, with his own blood, on the Shanshu Prophecy, thereby revoking his part in it.

Spike: “What do you think all this means for that Shanshu boogaboo? If we make it through this, does one of us get to be a real boy?”
Angel “Who are you kiddin’. We’re not gonna make it through.”