((ooc: it's totally natural for him to have forgotten a lot, since they didn't talk about it much, and I was expecting that! Kaworu is just being a jerk.))
Uniting it and yet ending it - that's a good explanation. Lilim would take on a new, singular form and consciousness, leaving the Earth to the Angels, who were originally meant to colonize it.
[Another casual sip of his coffee.]
That was my job, as things played out. And that's one of the main things Acumen took exception to, calling it 'genocide'. But it's as natural to Angels as breathing, so removing that need leaves you with a rather pathetic creature.