Just as being born with a physical body on this earth doesn't mean one understands everything about it, dying doesn't mean one understands everything about the spiritual world either.
Literal
People [subject-が] physical-body [object-を] having, on-earth [to-に] born [just-because-からといって], earthly things [object-を] all understand [it-is-not-the-case-that-わけではない] [same-as-のと同様に], died [just-because-からといって] spiritual world [object-を] all understanding [it-is-not-the-case-that-わけでもない] [explanatory-のです].
A densely layered philosophical sentence. The core pattern is A-のと同様に-B ('just as A, so too B'), where both A and B use ~からといって…わけではない ('just because X doesn't mean Y'). The second clause mirrors the first but substitutes わけでもない (with も adding 'either'). 肉体を持ち uses the verb-stem connective form (持ち) to link 'having a body' to 'being born' in a literary register. 霊的世界 ('spiritual world') marks the sentence as philosophical or religious discourse.