why is the concept of determism often regarded as more important than christianity.
I assume you meant the soft determinism as in William James.
Read this: http://www.informationphilosopher.com/freedom/determinism.html
We call this "soft" causality. Events are caused by prior (uncaused) events, but not determined by events earlier in the causal chain, which has been broken by the uncaused cause. Christianity is built on a foundation of "free will"