It is tremendously difficult to summarize a religious tradition that has developed worldwide for two thousand years. Christianity is the largest religious group in the world, with over 2 billion followers, roughly one-third of all the people in the world. Although the largest number of Christians is in the United States, that number has begun to decline, although there has been tremendous growth in Africa and Latin America.
Historically, the three main “families” within Christianity have been the Catholic Church, the Orthodox Church, and the Protestant Churches. In addition, there have been thousands of sub-groups, sects, and religious movements. These groups differ widely in beliefs, practices, worship, and organization.
It is useful to understand that all Christian groups shape their beliefs and practice from four key sources: scripture (the Bible and its interpretation); tradition (the doctrine, authority and structures of the group); experience (the life of believers and the church in prayer and action); and reason (reflection and conscience). Depending on the relative importance of each of these, Christian churches will look very different from each other. For example, Evangelical Protestants focus mainly on the Bible as their guide, Roman Catholics may look to church teachings and the teachings of the Pope and bishops, and Quakers will center on the “inner light” that each individual bears.