Simplify the following text for a Grade 14 native English-speaking person.
Original: The movement 's purpose was to reaffirm orthodox Protestant Christianity and zealously defend it against the challenges of liberal theology , German higher criticism , Darwinism , and other movements which it regarded as harmful to Christianity .
Simplified: The movement 's purpose was to reaffirm key theological tenets and zealously defend them against the challenges of liberal theology and higher criticism .