This always confused me, as we see during the war of the ring Glorfindel stays at Rivendell and really doesn't do much else, was he sent back in an Istari styled mission in middle earth and was he granted more power. But of all the elves to send back why Glorfindel when the Valar could sent the likes of fingolfin, Ecthelion and so on.
So why was Glorfindel sent to Middle earth and what was his mission?
These paragraphs explains in more detail why Glorfindel was sent back.
Glorfindel’s spirit passed to the Halls of Mandos, where he waited with the spirits of the other Noldor who had died during their war against Morgoth. But because of Glorfindel’s noble actions in life, his reluctance at the Exile, and his furthering of the purposes of the Valar by saving Tuor and Idril, he was re-embodied after only a short time. He had redeemed himself, and was purged of any guilt. Not only did his sacrifice get him an early pardon, it earned him great powers, so that he was almost an equal to the Maiar.
Eventually, Manwë sent him across the sea to Middle-earth, possibly as early as Second Age 1200, but more likely in 1600 with the Blue Wizards. If the latter date, he arrived just after the One Ring had been forged, Barad-dûr built, and Celebrimbor dead or soon to be so. While the Blue Wizards were sent to the east, Glorfindel’s mission was to aid Gil-galad and Elrond in the struggle against Sauron. He played a prominent behind-the-scenes role in the war in Eriador and the other struggles of the Second Age and Third Age. His part, though great, was mostly overlooked by the histories, because his immense, angelic power was not usually displayed openly.
Referred from http://tolkiengateway.net/wiki/Glorfindel#Re-embodiment_and_Return
The general consensus is that it is the same person, given the uniqueness of Elven names. As to the reason, there are two points. First, Glorfindel was a powerful elf, on par with those mentioned. He was, it seems, sent back (contrary to the rules the Valar had made) to bring the Elfstone, so that Elessar (Aragorn) could fulfill his destiny, should the he succeed.
The actual reason isn't really known. Tolkien never got around to fixing this rough spot in his histories. They were not originally supposed to be the same, but Tolkien's evolving thoughts on elves left him with a quandary he never solved.
