[Thingol]

In the section about the Istari in the Unfinished Tales it says that the Istari all swore allegiance to the sun, which was a representation of the power of Iluvatar. Although how the sun is a representation of the power of Iluvatar escapes me. As has been said the sun is the last fruit that the tree of Laurelin bore. It was set in a vessel, hallowed by the Valar, and guarded by the Maia Arien. The only reason I could think of, for the sun being a symbol of Iluvatar, is it is the brightest object in Middle Earth; it mirrors the flame imperishable that Iluvatar set to burn in the center of Ea. Although the sun is a relatively new creation, compared to the flame imperishable at least. So in effect, Gandalf is a wielder of the power of Iluvatar and also a servant of it.