(An AT field is something every human being on earth has. “The divine boundary that humans cannot violate, the light of ones soul it’s the AT field everyone possesses in their heart”.)
“Why is this live action?”. Well that’s simple, it’s to make Shinji’s reality feel more like it ever has. It’s the difference what we saw earlier in the movie.
And Rei tells him that he’s right it’s a dream. And so Shinji tells her; “So I’m not here either”.
And this brings another message. Human communication is violent and messy. But it can also be loving. And so Shinji stops choking her when she puts her hand on his face.