As all Eva nuts know, Eva was the propagator of all of humanity, as Adam was the Propigator of the Angels. All humans are made from LCL, her blood, held together by theeir AT Fields. All humans must eventually return to Lilith. That time is third impact. During Third impact Rei fused with Lilith, and with Shinji almost caused complete human instrumentality, until Shinji rejected it, causing Lilith's head and arm to fall off her body, leaving only Shinji and Asuka alone on Earth to be the new Adam and Eve of Humanity.
I hope to god that you had already watched End of Evangelion before reading this, major spoilers. Also if your don't get what the hell I'm talking about, google Neon Genesis Evangelion. Lilith by the way is also of course, the first woman created in the hebrew bible, who rebelled against Adam and god, and went on to be a total slut and kill babies.