Unlike his predecessor, Jaime Reyes was chosen to wield the powers of the scarab by the scarab itself. Though at first it was hard to controls the scarab's powers and abilities, not to mention its personality as it was a living thing, Reyes would eventually gain full control and become the true Blue Beetle.
For him, one of the greatest challenges was to overcome what the Beetle actually was. It was a living weapon sent by a group of beings known as The Reach. They use the beetles to scout other worlds, and then take them over. Jaime's was slightly damaged though, and thus it forgot this key aspect of its programming.
Under Batman's wing, along with other heroes, they helped Jaime and the beatle defeat the Reach, and truly welcomed them into the hall of heroes, where Jaime serves faithfully still.