Why Voldemort wanted the Prophecy in Harry Potter and the Order of Phoenix

After coming back to a physical form of life in the 5th instalment of the Harry Potter franchise, The Order of Phoenix, Voldemort plans to obtain the prophecy of the chosen one who was prophecised to kill him. In the Wizarding World of Harry Potter, prophecies are predictions of the future, which are somehow recorded into spun-glass spheres and stored in the Department of Mysteries' Hall of Prophecy. To complete this task, Voldemort chooses his loyal follower and father of Draco, Lucius Malfoy.

The reason Voldemort wanted to obtain the prophecy goes way back in the story when Harry was just about to be born. Before Harry's birth, Prof. Dumbledore had gone to interview Sybill Trelawney for a job at Hogwarts. During the interview, Sybill Trelawney foresaw a prophecy: the prophecy of the child being born who'd have the power to put an end to Voldemort. One of Voldemort's most loyal and powerful spies, Prof. Severus Snape overheard half of the prophecy and told the Dark Lord about it. 

Prof. Sybill Trelawney
a still from Harry Potter and the Order of Phoenix

The prophecy goes as: The one with the power to vanquish the Dark Lord approaches ... born to those who have thrice defied him, born as the seventh month dies... and the Dark Lord will mark him as his equal, but he will have power the Dark Lord knows not... and either must die at the hand of the other for neither can live while the other survives ... the one with the power to vanquish the Dark Lord will be born as the seventh month dies…

The prophecy talked about how Voldemort will mark him his equal and only then will he have the power to destroy him but Snape only heard the beginning of it. He never heard anything about Voldemort marking the chosen one as his equal. Unaware of this, Voldemort approached Harry, who he thought the prophecy was about, to kill him before he grew strong enough to be able to oppose him. This cost Voldemort everything as his killing curse rebounded from Harry because of his mother's sacrifice for him. 

Voldemort comes back to life
a still from Harry Potter and the Goblet of Fire

After coming back to life, Voldemort knew he had done something wrong and wanted to know the whole prophecy before making any move. That is why he sent a group of death eaters, led by Lucius Malfoy, to obtain the prophecy from the Department of Mysteries' Hall of Prophecy.

The whole 5th part is based on Harry Potter training the next Order of Phoenix and Voldemort trying to acquire the sphere in which the prophecy was stored.

____________________________________

Warner Bros. is currently working on Harry Potter's prequel series, the Fantastic Beasts which tells the story of Dumbledore and his lover-turned-enemy, Gellert Grindelwald.