Complex sentence: To justify his claim Saint Paul cites Epimenides' poem, perhaps just a bit of humor, because Saint Paul quotes a Cretan person to prove that Cretans are always liars.
Split into simpler sentences: To justify his claim Saint Paul cites Epimenides' poem. This may be a contradiction, or perhaps just a bit of humor, because Saint Paul quotes a Cretan person to prove that Cretans are always liars.