Severus Snape had only tried to save James Potter.
 Snape's memories also provide Harry with the information he needs to ensure Voldemort's final defeat, in the form of conversations Snape had with Dumbledore
Snape's memories then reveal that Dumbledore had impetuously tried to use the Gaunt ring, which had been cursed by Voldemort, and had been suffering from a powerful curse

