Why was Christianity so roundly criticised in the Enlightenment ?
During the Enlightenment, Monarchs across Western Europe espoused that they were obeying direct orders from God.
The so-called divine right of kings justified the king's absolute authority in all matters, both sacred and secular. It was impossible to criticize the king without criticizing God, and vice versa. Those who spoke against the Church found themselves imprisoned by the government, which used biblical scripture to denounce revolutionaries. In short, governmental rule and religious faith were intertwined.
Again, intellectuals of the Enlightenment era fought this repressive situation by using logic combined with reason, which included common sense combined with observations. The sciences expanded as they developed scientific methods that involved testing hypotheses by executing repeatable and verifiable experiments. Moreover, universities and publications made available to the general public helped popularize science and rational thought.