The following 45 minute video by R C Sproul will provide you with an excellent understanding of theological liberalism. You will then be able to see just how Christendom has become corrupted by it, as it has been around since the late 1800s.
In the course of explaining liberalism, he gets into Pelagianism, semi-Pelagianism, Arminianism, and orthodox reformed doctrine. His explanation will give you insight into what is wrong with not only liberal churches, but the emergent church, Catholicism, Rick Warren’s (and the many others) who propagate the social gospel, and more.
This video should be basic Christianity 101 for all new Christians.
The founding of the Orthodox Presbyterian Church:
The Orthodox Presbyterian Church was founded on June 11, 1936, in the aftermath of the fundamentalist-modernist controversy, under the leadership of J. Gresham Machen (longtime professor of New Testament at Princeton Theological Seminary, who also founded Westminster Theological Seminary in 1929). With the infiltration of theological liberalism, the mainline Presbyterian Church in the USA had departed from historic Christianity, including the rejection of doctrines such as the inspiration and authority of Scripture, the virgin birth of Christ, and the substitutionary atonement. Originally calling itself the Presbyterian Church of America, the young church was forced by the threat of a lawsuit to change its name in 1939, and it adopted the name Orthodox Presbyterian Church.
To continue reading https://www.opc.org/historian.html