Friedrich Shleiermacher was the "father of liberal theology." In essence, he presented a lot of new problems to conservative Christianity.
This is hugely significant, because liberal theology opens up room for The Bible, the infallible word of God, to be taken as fallible. This allowed Enlightenment Christians to reconcile their faith with convictions about science and worldly ethics.
I believe he opened a kind of flood gate. He opened the door for those who claimed to be Christians, but fundamentally changed the nature of what it means to be a Christian.