And Ilúvatar spoke to Ulmo, and said: 'Seest thou not how here in this little realm in the Deeps of Time Melkor hath made war upon thy province? He hath bethought him of bitter cold immoderate, and yet hath not destroyed the beauty of thy fountains, nor of thy clear pools. Behold the snow, and the cunning work of frost! Melkor hath devised heats and fire without restraint, and hath not dried up thy desire nor utterly quelled the music of the sea. Behold rather the height and glory of the clouds, and the everchanging mists; and listen to the fall of rain upon the Earth! And in these clouds thou art drawn nearer to Manwë, thy friend, whom thou lovest.'
Then Ulmo answered: 'Truly, Water is become now fairer than my heart imagined, neither had my secret thought conceived the snowflake, nor in all my music was contained the falling of the rain. I will seek Manwë, that he and I may make melodies for ever to my delight!' And Manwë and Ulmo have from the beginning been allied, and in all things have served most faithfully the purpose of Ilúvatar.
In this conversation, which takes place before Ilúvatar creates the world described in the Music of the Ainur, we see shown forth the first example of Ilúvatar's warning to Melkor that anyone who 'attempteth [to alter the music in my despite] shall prove but mine instrument in the devising of things more wonderful, which he himself hath not imagined' (17). Ilúvatar then repeats this warning to Melkor in the moment he grants the Ainur a Vision of their Music (17), and while the text tells us that he said 'many other things' (17) to them at this time, we get to hear only his words to Melkor and Ulmo. They are thus singled out, and Ilúvatar's words to them bookend the Vision, with Melkor addressed directly before it and Ulmo directly afterwards.
While Ulmo responds with wonder and delight and declares his intention to collaborate with Manwë, as we saw, Melkor is for now silent and 'filled with shame, of which came secret anger' (17). The next (and last) time he speaks in the Ainulindalë follows immediately upon the entry of the Ainur into the newly made world:
And in this work the chief part was taken by Manwë and Aulë and Ulmo; but Melkor too was there from the first, and he meddled in all that was done, turning it if he might to his own desires and purposes; and he kindled great fires. When therefore Earth was yet young and full of flame Melkor coveted it, and he said to the other Valar: 'This shall be my own kingdom; and I name it unto myself!'
Melkor's stated intention of course provokes a refusal to submit from Manwë -- 'This kingdom thou shalt not take for thine own, wrongfully, for many others have laboured here no less than thou' (21) -- and leads to war between Melkor and the other Valar.
What's most striking to me in all of this is that the beauty of water described in its various forms arises from the unintentional collaboration of Melkor and Ulmo. Melkor's hostility and selfish desire to dominate the Music has worked upon water to produce beauties 'fairer than my heart imagined,' as Ulmo recognizes. And precisely as Ilúvatar predicted. It should also stand out because it is the only time (I can think of off the top of my head) when Melkor's evil actions produce unquestionable, inspiring beauty untouched by any sorrow. It is a perfect example of the later statement that evil will prove good to have been, and yet remain evil (98). In that thought, however, there can be only sorrow, because Melkor cannot see the beauty he has helped to create, cannot be inspired by it to collaborate with Manwë, his 'brother ... in the mind of Ilúvatar' (21), cannot, therefore, repent of his desire to dominate. Far from it in fact: 'Melkor hated the sea, for he could not subdue it' (30).
Clearly there is more work to be done here. A study of the meaning imparted by the way the Ainulindalë is structured looks like it could provide some intriguing results, given what we've seen here. I have skipped over the appearance of the Children in the Vision, for example, as well as the perhaps metaphysical implications of the question of why it is that water becomes more beautiful as a result of the effects of evil. Is it because it is the part of creation which best and most preserves the Music of the Ainur, and therefore the primordial thought of Ilúvatar as expressed in the themes he propounded to them?