1) First of all, is a God that purposefully limits himself/herself/itself any less omniscient than one that does not? They both have the same power, but one uses it differently.
2) God does not test my faith for his own knowledge, but so that I may know its depth.
3-5) Some Christians don't believe that the flood was a historical event (like me) but rather a story to show a Biblical truth.
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"Science without religion is lame; religion without science is blind." - Albert Einstein