Melian among the maia

[Inziladun]

Belegorn's remark brings the question of the purpose of the "spell" that was laid on Thingol when he and Melian met. And who was responsible?

To the second question, I would say Melian did it. We later see Morgoth having the power to arrest physical change in Húrin (he could not die while Morgoth's power was on him), so it seems plausible Melian could have had a similar ability. And it seems the spell was for Thingol alone.

[Melian] spoke no word; but being filled with love Elwë came to her and took her hand, and straightaway a spell was laid on him, so that they stood thus...

But why? Some sort of "enhancement" or ennoblement for Elwë, to prepare him for being the spouse of a divine being? He is obviously changed when next seen by his followers.

[Elwë's] people gathered about him in joy, and they were amazed; for fair and noble as he had been, now he appeared as it were a lord of the Maiar...

The Silmarillion Of Eldamar

So he seemed to have been elevated from his previous stature. Was that just a requirement for matrimony? Sheesh. Women always want to change a man...