Approximately one-third of all people in the world belong to the Christian religion. There is no question that as a religion, Christianity is one of the largest and most powerful forces on the planet - indeed, it would probably dominate the planet if it were not for the fact that it is divided in so many different ways. But what sort of religion is Christianity?
There are many different classifications of religion, each with their own particular characteristics that distinguish them from one another. They are not, however, mutually exclusive - any one religion can be a member of several different categories at the same time. Understanding the nature of Christianity and Christian belief can be greatly aided by having a better understanding of how and why it belongs to different religious groupings.
Although many Christians feel that they can see or experience God in nature or through natural events, Christianity doesn't qualify as a nature religion doctrinally. Nothing in traditional Christian theology suggests that the primary way to find and experience God is in nature. Some fringe expressions of Christianity may lean more towards nature religions, but they are a tiny minority.
In a similar sense, Christianity also isn't really a mystical religion. Granted, many individual Christians have had mystical experiences and these experiences have, in turn, played important roles in the development of Christianity over the centuries. Nevertheless, such experiences are not encouraged for the rank-and-file Christians.
Finally, orthodox Christianity isn't a prophetic religion, either. Prophets may have played a role in Christian history, but most Christian believe that God's revelations are complete; therefore, there technically isn't a role for prophets to play today. That isn't true for some Christian denominations - for example Mormons and, perhaps, Pentecostals - but for most that follow traditional Christian teachings, the era of prophets is over.
We can count Christianity as a part of three other religious groupings: sacramental religions, revealed religions, and salvation religions. The latter two apply most generally: it would be difficult to find any form of Christianity which does not qualify as a revealed or salvation religion. It is arguable, however, that it may not be quite appropriate to describe some forms of Christianity as a sacramental religion.
Most forms, and certainly most traditional and orthodox forms, do place a very heavy emphasis on sacramental rites and ceremonies. Some, though, have eschewed ceremonies and priests as cultural artifacts that simply don't belong to the way Christianity originally was or should be. If these forms still qualify as sacramental religions, it is only just barely.
Christianity is a salvation religion because it teaches a message of salvation which is supposed to apply to all of humanity. How salvation is achieved varies: some forms emphasize works, some emphasize faith, and some argue that salvation comes to all, regardless of the actual religion they follow. Whatever the exact circumstances, though, the long-term purpose of life is generally treated as reaching salvation and God.
Christianity is also a revealed religion because it traditionally focuses heavily upon revelations from God. For most Christians, the entirety of those revelations can be found in the Bible, but some Christian groups have included revelations from other sources as well. It's not important where those revelations happen to be collected; what is important is the idea that they are a sign of an active god who is very much interested in what we do and how we do it. This is not a Watchmaker God who is simply observing us, but instead one who has taken an interest in human affairs and intends to direct us on a path deemed appropriate.
In traditional Christianity, salvation, revelation, and sacrament are all deeply intertwined. Salvation is communicated via revelation while sacrament provides a visible sign of the promise of salvation. The exact content of each step will differ from one Christian group to another, but in all of them the basic structure remains relatively stable.