For now, I'll begin with something very embryonic and probably obscure, sparked by the introduction to Badiou's Briefings on Existence, and fueled by a summer of reading several books by Žižek.
It may well be that God has been agonizing for a very long time. What is surely less doubtful is how, for centuries, we have been busy with successive ways of embalming Him...Taking seriously the death of God does not result in the vulgar atheism committed to the claim that God "does not exist", that it is a fiction, a social construction or symbolic function. Nor do we fall into agnostic limbo, unable to decide. God is not explained away as an abstract concept with no real and/or confirmable existence. As Badiou says,
I take the formula "God is dead" literally. It has happened. Or, as Rimbaud said, it has passed. God is finished. [Badiou, Briefings p24-5]
If "God is dead" is asserted, it is because the God spoken of was alive and belonged to the dimension of life. When you consider a concept, a symbol, a signifying function, you can say that they have become obsolete, contradicted, and inefficient. They cannot be said to have died. [ibid p24]When we say "God is dead", we unrepentantly affirm that God was, God existed, lived, and has now passed. God is a reality, a real existence or mode of existence, that has decomposed. What was this mode, this real thing that God had been?
Here we can take some direction from Deleuze's remarkable book on Foucault [sidenote: a book which, for me, is of the utmost importance in reading Deleuze's works as a whole, from D&R and LoS to the latter writings with Guattari; more on that later]. Deleuze there describes this existence as that of a certain formalized combination of forces; specifically, of those forces of which human beings are capable. God, or the "God-form", is a real thing, just as much as you or I: for Deleuze, everything, every mode of existence, is an arrangement of intensive forces whose consistency ('thing-ness', to be crude) is maintained insofar as these forces do not surpass certain limits, remaining within "non-decomposable variable distances" in relation to each other. Every combination or arrangement (agencement, assemblage) of forces is metastable within its limits. Yet if these distances do decompose, if the relations between forces reach the critical point at which a limit loses efficacy and a threshold is crossed, we then pass into a new arrangement, a new distribution and metastability with new limits.
Any arrangement or mode can thereby be understood by its immanent limits and the tendency of its constituent forces to respect these limits. If we accept that every individual mode is unique, different from every other, singular (and the reasons for doing so are by no means self-evident), then the mode itself is defined as a singularity. A singularity is not merely a unique thing; it is precisely that which is expressed in the tendency of forces to 'posit' and respect limits immanent to their given unique arrangement. Singularity is not simply the uniqueness of terms within a diversity, but the tendency by which "the given is given as diverse" to paraphrase D&R.
The singularity of a mode is thus the unique configuration of forces and their limitations that compose a thing as consistent and metastable, but moreover it is the tendency immanent in the forces so combined toward that metastability. The mode qua arrangement is a multiplicity of singular points toward which the forces arranged tend; as DeLanda describes it in his Intensive Science & Virtual Philosophy, it is a topological diagram or vector field within which are inscribed various attractors defining the long-term tendencies of the individuated trajectories/forces. When a force exceeds the 'basin of attraction', the diagram bifurcates, and a new distribution of singular points results, along with a new set of limits and tendencies immanent to the resulting re-arrangement.
The God-form is, on the one hand, such a mode, defined by an immanent diagram of potential permutations of constituent forces. The forces involved are all the individual and collective forces of human beings. Yet what makes the God-form distinct from other possible arrangements of these forces, other possible ways we might exist? The God-form names precisely the formalization of a particular mode such that there is a strict division between two generic forces: the general forces of the human life-world, and the divine forces of 'raising to the infinite' or of realizing perfection. In this way, the former forces become the brute matter whose formation corresponds to the latter, which becomes a formalized function expressed by this formation. Man is born as the Content, submitted to a finite form, only functioning through the Expression of God as the infinity of formalization.
To bring things down to earth: God exists when the immanent limits of human beings become autonomous, external, as a formalized system to which they are submitted, a transcendent imposition of function. It is not simply that people 'reify' their social relations onto some imaginary being; as with Marx's notion of the commodity form, God is an 'objectively necessary appearance' - we may be the 'real' causes of our various functions, but God is a quasi-cause that appropriates all of these functions, formalizing them and reducing our 'non-reified' causality to a subjective illusion. With formations like the God-form, the Man-form, the State-form, the Organism, etc, the organization of forces is no longer immanent to the arranged forces, but becomes autonomous of and reacts back on what it organizes. (Strangely enough, this definition corresponds to that of 'institutions'; this problem is very important for my Div III research, and I'm not really prepared to address it appropriately, but I will say I believe the crucial thing about focusing on institutions in economics is to rediscover in them the forces they formalize, to reintroduce strategy at the heart of stratification.)
As Deleuze never fails to remind us, we should not be too quick to rejoice in affirming the death of God, as a new formalization was already waiting to replace him: the Man-form (for more on this, see the appendix to Deleuze's Foucault). Yet, following Foucault, we should realize the futility of now plotting the assassination of Man, as if our Fall from Grace requires a redemptive sacrifice. In a Hegelian way, Foucault understood that the death of God, far from signaling the new reign of Man, was already the death of Man from the very beginning. As soon as Man seized the empty throne of divinity, his fate was sealed. Fidelity to Man does not do justice to God's death, to what God died for: if God has died, it was not to clear the way for Man's reign, but to warn us that this place that Man will fill is a place of death, that Man, too, will die, and that we must already see in Man that which will overcome him, destroying not only God and Man, but the very place they both occupied (the surface qua plan of organization or plane of transcendence).
When Christ dies on the cross, it is at once the death of God and of the Man who takes his place. This is perhaps what is crucially missing in Paul. If we affirm that God is dead, we should do justice to this death; we should be faithful not to the corpse or the ghost, but to the event of death itself. God died not to set Man free, but to free that which was lost to them both, that which may overcome them: the unlimited (af)finity of the singular in its becoming.