After this time jump, when Roy found that he had come to the period of the War of the Ancients, he roughly realized what he had to do in this time node.
Of course, his understanding of what he wanted to do came from some historical events that later generations had learned. From beginning to end, Roy was strictly following the historical line. The purpose of doing this was naturally to ensure that he could successfully complete the closed time loop and play the final notes of the Movement to the End of Reincarnation.
In other words, in a sense, the infinite dragon Murozond's plan had failed. He had exiled Roy into the spacetime flux because he wanted to use Roy's demon nature to disrupt the timeline arbitrarily. But Roy's restraint of his actions exceeded Murozond's imagination. This instead fulfilled the bronze dragon Nozdormu's goals because Roy had also become a 'protector' of history.