I don't know if it is well supported, but it could be slightly supported by the text and the happenings in LotRs that when
Gandalf returned as "
the white" his restrictions were removed or at least lessened by the
Valar. This could be for two possible reasons:
A. When the Valar sent the
Istari (I don't know the year) the threat from
Sauron was judged to be best handled by the
Men and
Elves who at this time had a stronger military presence and also greater leaders. When Gandalf returned the Elves were waning and the men had been without a declared king for sometime. It is only after Gandalf's return that
Aragorn claims his birthright and strives to reunite mankind under his banner. Even so, his forces were pitiful when compared to those led by
Elendil and Gil-Gilad. Hence the need was now greater and limitations were removed.
B. I'm not going to suggest allegory here, but I think we will all admit that
Tolkien was influenced by Christian ideas and one such idea is of a perfect entity passing the ultimate test, paying the ultimate price, and returning in a more openly powerful form (not necessarily a more powerful form, but in a form with less limitations as to when and how he can reveal his power).
In Christianity Adam fails a test and suffers a loss of purity and immortality. Thousands of years later, another entity emerges, is put to even more strenuous tests culminating with the loss of his life for others, and by enduring the ultimate humiliation (execution as a blasphemer/criminal/liar) breaks the bonds upon all humanity and returns as the revealed Son of
God to preform greater more obvious miracles than he had pre-death.
In Tolkien we have multiple incidences of entities failing tests. The
Numenoreans fail their test.
Isildur fails his test . . . but also, with the exception of Gandalf (and possibly Radaghast. He's a bit of an anomoly because while he didn't go bad, he didn't do a heck of a lot of good either.), every Istari seems to have failed their test.
The illusive
blue wizards are said to have fallen, possibily they started
evil cults (or possibly they did not and were martyered even as Gandalf, but we are left with an untold story there).
Radaghast was seduced by peace, I would say. He found a comfortable niche in
Middle Earth and stayed there and as much as I like the idea of a Dr. Doolittle-ish Wizard talking to the
animals for eternity, it really isn't what he was sent to do (I've heard otherwise theorized, but I'm going with the slacker theory for the sake of my theory.)
And
Saruman was the most obvious failure. He was seduced by power. He even makes an attempt to "recruit" Gandalf and so doing provides another temptation.
Gandalf's Temptations:
1. Radaghast style: Gandalf liked comfort. He was concerned with the little folk partially because he was comfortable around them. He liked amusing people with fireworks. He had a niche he could easily have slipped into.
2. Sarumen style: Unlike Saruman who fell to ring lust through lore alone, Gandalf frequently had
the ring within his grasp and was once directly offered it.
3. Blue wizard style: Gandalf's
travel was as extensive as his blue-brethren. Any temptation they would have endured, he would have endured.
This is followed by a sacrifice.
Logically, it does not make sense for (arguably) the member of the fellowship with the most value to be
the one who is lost first (well, from a literary point it makes a ton of sense because it provides the greatest tension. I mean, if they had lost
Pippin they might've had a sad speech, but up to that point he had been more of a liability than an asset). Gandalf held the greatest power.
Four of the members of the fellowship were proven warriors. It is very possible that
Boromir or
Legolas could have put up enough of a fight against the
Balrog to delay his advance and allow the remaining fellowship to reach the far gate unhindered (Though I don't believe any of them would have had a chance of suceeding and it is possible that the delay would have only been minimal. We don't have a lot of examples of mortal to Balrog combat). At the very least you could have lined up
Merry, Pippin, and
Sam on the bridge and hope he took some time to season and roast each meal in turn before continuing on after the other six.
However, Gandalf, without hesitation, faces a foe who will most likely destroy him. He experiences a mortals death and his immortal nature returns to the Valar. . . and we know what happens next.
In Christianity the purest being is sacrificed in place of sinful beings in a dramatic reversal of justice. It must've seemed to the disciples that they had suffered an irreversable loss. They had lost the only one among them with power to raise the dead, heal the sick, draw thousands to his word and then feed them with minimal supplies. Very similar again.
But I'm not trying to prove allegory here. I'm just going with suggested inspiration.
Perhaps now risen, Gandalf has proven that he is deserving of the power he had been required to hold back, the power that had seduced one (and possibly three) of his brethren. He had proven that he would not use power to dominate but rather to protect. He had proven he would sacrifice his own life and all the potential for power (I'm guessing it would be much easier for an Istari to set up a private kingdom in Middle Earth than in
Valinor) to aid those weaker than himself.
So here the similarities sort of diverge. Rather than being a perfect sacrifice that redeems other imperfect beings, Gandalf would be a powerful sacrifice that is elevated to a higher level of power.
I don't know if this holds water, but I think there is some semblence to the two stories. Not allegorical, but definitely one is a weak shadow of the other.