Complex sentence: The concept of post-monotheism has similarities to the "transtheistic" ideas of Paul Tillich, as well as possibly open theism, though its program is decidedly different from the existentialism of the former and the evangelism of the latter.
Split into simpler sentences: The concept of post-monotheism has similarities to the "transtheistic" ideas of Paul Tillich, as well as possibly open theism. However, its program is decidedly different from the existentialism of the former and the evangelism of the latter.