Although Chaos can be studied in terms of antecedents in classical literature and philosophy, its appearance in [Paradise Lost] owes its problematic character to Milton's theology. Chaos is infinite, and filled by a ubiquitous God who has nonetheless withdrawn his creative will from chaotic matter (7.168-73). None of the categorical binaries established during the creation of Genesis inhere in Chaos. It is neither this nor that, "neither sea, nor shore, nor air, nor fire,/ But all these in their pregnant cause mixed/ Confus'dly" (2.912-14); therefore Satan, as he traverses this indeterminate space, confusedly mixes locomotions, "And swims or sinks, or wades, or creeps, or flies" (2.950). The "embryon atoms" (2.900) of Chaos are "the womb of Nature" (2.911), the pure potential that the Son first circumscribes with golden compasses when creating our universe (7.225-31) and will doubtless use again in creating new worlds (2.915-16). Chaos cannot be good until God has infused it with creative order. It is at least morally neutral, at best thoroughly praiseworthy, as a part of the process by which God makes and sustains all things.
But alongside the language of atomism, Milton gives us a mythic Chaos, personified as the ruler of his realm, or rather its "Anarch" (2.988), since Chaos is by definition without rule. This Chaos, speaking for his consort, Night, and for a shadowy pack of Hesiodic creatures and personifications (2.963-67), expresses his resentment over recent losses (the creations of Hell and our universe) and supports Satan's mission on the assumption that "Havoc and spoil and ruin are my gain" (2.1009). We thus arrive at a paradox. Theologically, Chaos is neutral or better. Mythically, in terms of the epic narrative, Chaos is the ally of Satan.
Kerrigan, Rumrich, & Fallon, intro. to Paradise Lost (2007: xiv-xv).