Zelda often uses direct contrasts, and this is no exception. Ghirahim acts as the contrast to Fi, with essentially the same mission; he is preparing the rise of the villian who will wield him, and Fi preparing Link to become the first hero to weild her.
SS is meant to be the archetype for all the later set games that ironically came before it.
From a story perspective this also mirrors the contrast between the hero Link and anti-hero Gannon seen later. The triforce can only be used by mortals, and in this way Gannon becomes the vehicle to deliver an ironic death to Hyrule. The only true difference then between Gannon and Link is what lies in their heart.