(If you already know this stuff, do skip it, pausing only, please, to tell me where I've got it round my collar.)
Dynamic systems are highly sensitive to initial conditions. So even if the system's future behaviour is fully determined by their initial conditions, (planetary orbits) with no random elements involved, the fact that they are deterministic does not make them predictable if the initial conditions are made approximate by tiny changes.
Tiny initial changes can result in huge and unpredictable later results - the so-called "butterfly effect." The idea that a butterfly flapping its wings could result, weeks later, in the birth of a hurricane. Although we know the components of a hurricane's birth, we can't predict its emergence because it is dynamic, complex, and sensitive to tiny initial changes.
"Chaos: When the present determines the future, but the approximate present does not approximately determine the future." says Edward Lorenz.
All of the above I owe to Wikipedia.
Next, I'll get on to God. For that I'll need both chaos theory and the idea of emergent properties.
(I've got that nasty feeling that any readers will think "she's getting excited about stuff that's actually pretty common-place and widely-known." Maybe so, Mr Big Brains, but writing this stuff makes my head hurt so it must be good for me...)