Ah, Lilium. Such an amazing opening. The lyrics are from prayers if I recall correctly, and they're great too. Here's some handmade translation:
The mouth of the just will practice wisdom / and his tongue will utter judgement. / Blessed the man who endures temptation / Since, as he's being tested, he'll take the crown of life. // O Lord*, source of virtue / O Lord, divine fire, be merciful* // Oh, how holy, how serene, how kind / how lovely the virgin is believed to be. // Oh, how holy, how serene, how kind / how lovely, oh chastity lily
(*note: I'm translating "Kyrie" and "eleison" as "o Lord" and "be merciful" respectively, but the expression itself has deeper meaning in liturgy, due to the frequent usage. Refer to this.)
Spoilers about this song, for people who read the manga:
People often focus on how beautiful this song is (it is!), but they don't usually realise that it's directly tied to what happens across the story. It is not just some "random mass"; Lucy is the sinner here, asking for forgiveness. Granted, it isn't her "tongue" uttering judgement but rather her invisible arms, but still.
I'm also tempted to associate the "chastity lily" and the role of Virgin Mary in this prayer with Kouta, the deuteragonist (yup). It's a weird inversion of roles, but it works well - as in Catholic Christianity the Virgin Mary is not God, she is solely human, but she's expected to plea in defence of the sinner, just like a mother in defence of her child. And that's exactly what Kouta does for Lucy across the story, he is consistently taking her side, even if she's a diclonius; never by being forceful, but by being kind and serene. It's one of the few cases of a weak-willed boy in anime/manga that I feel justified. (Also due to his traumas.)
Also note how I'm calling Kouta the deuteragonist, even if people usually see him as the protag. The real protag is Nyuu/Lucy; that's her story, we're just seeing it from Kouta's PoV.
The manga is tragic and strange too, just like the anime. Okamoto Lynn always write weird but awesome stuff. However the manga contextualises better the struggle between humans and the diclonii and, more importantly - it delivers better the theme questions:
what exactly is a human being? what is a monster? Hard to say when both behave the same - sometimes being scum, sometimes being supportive, sometimes even sacrificing oneself for the sake of the others.
the old (but still valid) nature vs. nurture debate. How much is a monster born like one, and how much does society make one out of it?
I really enjoyed Elfen Lied back when I watched it. Even though it never really captured me again after that gruesome opening episode. Lilium is such a haunting OP, but then its contrast to the poppy ED is such a perfect microcosm of the show's wackyness.
It's been ages since I watched Elfen Lied and I still remember it and Lilium very vividly. A wonderful song. I have never found any similar OST in any other anime.
I loved the majority of the anime, but felt the ending should have been darker. Think I heard the maga went more in that direction, so need to check it out