Christian theology is the study of God from a Christian point of view. All Christians are united by the belief in Jesus Christ as the Son of God and as their savior. Beyond this point and, for many, the recognition of the Holy Trinity, the different strands of Christianity disagree over the finer points of Christian theology. The key points for discussion and disagreement are the nature of God and His relationship with Jesus and the Holy Spirit, the Eucharist, the Sacraments, and perhaps most importantly of all, the path to salvation.
The most important source of information regarding Christian theology is the Bible. There is debate over interpretations of the Bible because of translation issues; for example, the Greek word "repentant" has been translated into the Latin word "do penance" by the Catholic Church, which is why many Protestants discount penance as a sacrament. Other important texts include the letters or epistles of St. Paul, which are some of the earliest Christian writings. The Catholic Church also places high value on Church tradition.
The nature of God is one area most modern Christians agree on, though even then there are differences between those who believe in the harsher God of the Old Testament and the more humanist God of the New Testament. The largest area of agreement is on the dual nature of God as God and Christ, with many also believing the Holy Spirit to be God as well. Relatively small disagreements over the issue helped split the Catholic and Eastern Orthodox Churches.
The Eucharist is the commemoration of the Last Supper in which Jesus told his disciples that the bread in His hand and the wine in His goblet were His actual body and blood. The nature of the Eucharist is a hotly debated topic in Christian theology. Catholics believe in a literal transformation of both the bread and the wine called transubstantiation. Most Protestants either believe in a subtle transformation called consubstantiation, or believe that Jesus was being symbolic.
The sacraments are the seven most important rituals of the Church. Catholics believe in seven sacraments including marriage, baptism, penance, and the last rites. Most Protestants believe that the most important sacraments are baptism and Eucharist.
The nature of the cosmos and humanity's route to salvation are a big point of disagreement between Christians. The Catholic Church, for the most part, follows the teachings of Augustine of Hippo, who believed that, despite Christ's sacrifice, mankind was still sinful. Other groups have varying ideas for how people can get to heaven and whether God has already chosen who is saved or not.
Christian theology has not always been an open subject for debate. The first 400 years of development were characterized by disparate forces and factions, plus a lack of total power. Once enshrined in Rome, the Catholic Church began to clamp down on debates and theories that it did not agree with. This, for example, saw the end of Pelagian Humanism in the 4th and 5th centuries and also the Cathars in Medieval France. Open debate in Europe took centuries of often bloody combat to achieve.