What does Nicole mean by "make us whole again"?

[Uncle Jon]

She keeps saying that in the games, and I'm not certain by what she means by that. Or I am missing something very obvious lol.

[D:]

The hallucination of Nicole tells you right before you fight her:

Nicole: Yours is the last body we need to be reborn! The makers must be absorbed!

Isaac: "The makers"? You mean me? But Stross said we could destroy the Marker!

Nicole: Not if we consume you first!

So basically the Black Marker needs to kill and absorb you like all other forms of life on the Sprawl (thus "making Isaac whole with it") to trigger a convergence event and create a Brethren Moon[deadspace.fandom.com]. Their final goal is to make all living organisms "whole" by absorbing them to multiply - like every other type of Necromorph - which is why the Brethren Moons attack earth at the end of DS 3.