Part of the mind of Ilúvatar

[Formendacil]

So, I was rereading the Ainulindalë today, for the first time in a couple years (which is a bit of a shame, but not as bad as you'd think; I read it (and its HoME variants) so many times in my teen years that it's not exactly a forgotten text), and I barely got through three pages before I had a topic for the Downs.

While this is not a bad thing, I was supposed to be spending today outdoors...

Anyway, the following lines struck me:

Originally Posted by Tolkien, in the Ainulindalë,

But for a long while they sang only each alone, or but few together while the rest hearkened; for each comprehended only that part of the mind of Iluvatar from which he came, and in the understanding of their brethren they grew but slowly.

More especially, this was recalled moments later (over my second bite of breakfast) with this:

Originally Posted by Tolkien, in the Ainulindalë,

To Melkor among the Ainur had been given the greatest gifts of power and knowledge, and he had a share in all the gifts of his brethren.

This made me think... Melkor is alone, as far as I know, in being said to have a share in the gifts of all his brethern--a share, I would say, in part, with all the parts of the mind of Ilúvatar, This accords very well with what is generally said of him being the greatest of the Ainur, for example, in the following quote:

Originally Posted by Tolkien, in the Ainulindalë,

'Mighty are the Ainur, and mightiest among them is Melkor..

I trust that no one will say Eru is a liar.

Anyway, this got me thinking about Manwë, because there's always been a bit of tension in comparing him and Melkor. If Melkor is the mightiest in the thought of Eru, how can Manwë be called coëval with him?

More importantly... how can Manwë be considered "brethren in the thought of Ilúvatar" with Melkor? What is it about them that would cause Eru to say "you're brothers" in a way that they aren't with the rest of the Ainur? With Námo and Irmo (Mandos and Lórien) it makes sense, given their related fields of knowledge (related parts of Ilúvatar's mind from whence they spring): doom and visions. After all, if Melkor and Manwë are not like in power--and especially in Tolkien's later works, which the final version of the Ainulindalë is contemporary with, it is clear that Melkor is vastly the mightier, as Ilúvatar's statement affirms--how are they alike? It's not that they both spring from the same portion of Ilúvatar's thought, since Manwë is very clearly associated with the sky and winds, whereas Melkor is very clearly drawn from across the "elemental" spectrum, so to speak.

Any thoughts then, on how to reconcile this? I have one, also prompted by pages 1-3 of the Ainulindalë, but I'm curious what reconciliation others have attempted to make--if they have at all.