Why the hell am I even posting this? It's embarrassing that I spent so much time on something that can be very easily researched.

Although Christianity is the largest religion in the world, only about one out of three humans describes him- or herself as Christian. It thus follows that potentially two out of three or more are confused as to what it’s all about.

Key concepts

The Bible. The Christian holy text is called the Holy Bible. It is divided into the Old and New Testaments, which are further divided into between sixty-six and eighty Books, depending upon what branch of Christianity one is looking at. The Old Testament, also called the Hebrew Bible, is also a holy text of Judaism; the New Testament, also called the Christian or Grecian Bible, is unique to Christianity. For the first few centuries of Christian history the content of the Bible was in flux; since the fourth century, when Christianity became an official religion of the Roman Empire, the content of the New Testament has been a constant of twenty-nine Books and the content of the Old Testament has only varied slightly between denominations, with thirty-seven Books accepted by all as canonical. The Holy Bible was written from approximately 700 BCE to approximately 100 CE.

Theism. Theism, the belief in the existence of God, should need no explanation. It is the fundamental concept of Christianity, most strains of which subscribe to a form of pluriform monotheism. The doctrine of the Trinity states that God is three persons—God the Father, God the Son, and God the Holy Spirit-who-used-to-be-a-Ghost (subsequently I'll use the term 'Holy Ghost' because I like it better)—but one being. The expression of the doctrine used the Athanasian Creed (a Creed in use by the Catholic Church and widely accepted among liturgical Protestants) is:

Now this is the catholic faith: We worship one God in trinity and the Trinity in unity, neither confusing the persons nor dividing the divine being. For the Father is one person, the Son is another, and the Spirit is still another. But the deity of the Father, Son, and Holy Spirit is one, equal in glory, coeternal in majesty. What the Father is, the Son is, and so is the Holy Spirit. Uncreated is the Father; uncreated is the Son; uncreated is the Spirit. The Father is infinite; the Son is infinite; the Holy Spirit is infinite. Eternal is the Father; eternal is the Son; eternal is the Spirit: And yet there are not three eternal beings, but one who is eternal; as there are not three uncreated and unlimited beings, but one who is uncreated and unlimited. Almighty is the Father; almighty is the Son; almighty is the Spirit: And yet there are not three almighty beings, but one who is almighty. Thus the Father is God; the Son is God; the Holy Spirit is God: And yet there are not three gods, but one God. Thus the Father is Lord; the Son is Lord; the Holy Spirit is Lord: And yet there are not three lords, but one Lord. As Christian truth compels us to acknowledge each distinct person as God and Lord, so catholic religion forbids us to say that there are three gods or lords. The Father was neither made nor created nor begotten; the Son was neither made nor created, but was alone begotten of the Father; the Spirit was neither made nor created, but is proceeding from the Father and the Son. Thus there is one Father, not three fathers; one Son, not three sons; one Holy Spirit, not three spirits. And in this Trinity, no one is before or after, greater or less than the other; but all three persons are in themselves, coeternal and coequal; and so we must worship the Trinity in unity and the one God in three persons.

This doctrine is notoriously difficult to understand and is usually expressed using a diagram representing a non-transitive quasi-equivalent alternative logical system, called the Shield of the Trinity or Shield of Faith.

The Shield of the Trinity was developed in the thirteenth century and from a Christian standpoint is useful because unlike other visual metaphors for the doctrine of the Trinity, such as Venn diagrams or C.S. Lewis’s cube analogy, it does not lend itself easily to interpretations that are unorthodox from a traditional Christian perspective.

            If you think that St Patrick’s use of the shamrock to illustrate the Trinity doesn’t make any sense, you have grasped the principle.

God the Son, Jesus of Nazareth. God the Son is the central figure of Christian history and doctrine. He is identified with Jesus of Nazareth, a figure who lived in what is now Israel and the West Bank approximately two thousand years ago.

            It is historically certain that the man Jesus existed. Outside the Bible, he is referenced in Josephus’s Jewish Antiquities and somewhat unflatteringly in passing in the Talmud, as well as in several apocryphal documents dating from a very early period in Christianity. (Note: in Christianity it is considered proper to capitalise pronouns referring to God. Thus while the man Jesus is referred to in this essay using the pronoun ‘he’, Jesus as interpreted in Christian belief is referred to using the pronoun ‘He’.) Historical facts widely accepted about Jesus include: he was born between 7 and 2 BCE (the epoch of the common calendar is based upon his birth but was miscalculated) in either Bethlehem (south of Jerusalem) or Nazareth (in the Galilee region of northern Israel) to a woman commonly called Miriam or Mary. He was raised in Nazareth in a fairly standard Jewish family of the time. At a young age he was already a very learned legal and religious scholar who impressed the priests of the Temple with his insight. At some point in the late third decade of the first century Jesus became an itinerant healer and charismatic preacher able to attract large outdoor crowds. Some of his more radical views disturbed both Jewish and Roman authorities, who had him executed for sedition during the term of Pontius Pilate as Procurator of Judea (29-39 CE) and the reign of the Roman Emperor Tiberius (14-37 CE).

            The capsule of Jesus’ life given in the Gospels (the portion of the Holy Bible that deals with His life; the first four Books of the New Testament, called the Gospels According to Matthew, Mark, Luke, and John) is somewhat more detailed. As Leonard Cohen says, 'everybody knows that Jesus was born in Bethlehem without a single dime'. His mother, Mary, was the virgin bride of a widower named Joseph. Before Mary had lost her virginity she was visited by an angel who informed her that she had been impregnated by the Holy Ghost. Jesus was born in Bethlehem, the seat of Joseph’s family, during a sojourn there during an incredibly poorly-set-up census and tax season. Soon after his birth he was visited by nearby farm workers and a delegation of Zoroastrian priests from the Persian Empire (the number and names of the magi is not specified in the Bible but has traditionally been set at three—Balthazar from India and Melchior and Casper from Iran), who recognised Him as the prophesied divinely ordained King of Kings and Messiah (Messiah, a Hebrew-derived religious term for a saviour of the people and the faith, is rendered in Greek as Khrístos—hence ‘Christ’ and ‘Christianity’).

            Herod, the local ruler, perceived this prophesied King as a threat to his authority and ordered all baby boys in the area executed. Another angel informed Mary and Joseph of the danger, and they hid in Egypt until Herod’s death a while later, at which point they returned to Nazareth, where Joseph lived. Jesus grew up here and at the age of twelve got into a debate with the Temple priests during a family pilgrimage to Jerusalem.

            The next period of Jesus’ life appears to be lost to history, although Christian legends tend to have Him travelling extensively during this time. By the age of thirty He had returned to His homeland and was impelled to visit His cousin John the Baptist, a charismatic wilderness prophet who preached the abrogation of one’s sins via ceremonial immersion in the River Jordan. After this Jesus went on a vigil in the Syrian Desert, where evil spirits tempted Him with worldly power. He rejected their bribes and returned to civilisation ready to start His work as a religious leader. Jesus was by this point known as a highly intelligent and incisive man, so when He began His ministry, people were talking.

            Jesus’ first act was to declare the Year of the Lord’s Favour, the Jubilee. The Jubilee was a year, one out of every fifty, in which all property was returned to its original owner, all debts were written off, and the entire country mobilised in massive almsgiving. This threw the financial markets of the region into chaos, so regional authorities were quite understandably nervous that this man, who was already attracting a lot of followers, declared the Jubilee off of schedule. This seemingly hubristic act was their first intimation that this Jesus person may be more of a problem than the other crazy itinerant preachers in the area.

            Jesus’ ministry and teachings lasted for about three years before, during Passover Week, the Jewish and Roman leadership got scared and had Him brought in for sedition. Judas Iscariot, a member of Jesus’ inner circle, betrayed Him in the Garden of Gethsemane in exchange for thirty pieces of silver, whereupon Roman soldiers apprehended Him, gave him a show trial, and, the next day, executed Him by crucifixion. Unbeknownst to the authorities, this was the entire point of Jesus’ existing in the first place and, on the third day inclusive after His crucifixion, He rose from the tomb. He spent the next forty days with His eleven remaining Apostles (Judas obviously was not welcome any more and killed himself shortly after Jesus’ death), helped institute the structure of the early church, and then ascended bodily into Heaven. A week after this event the Holy Ghost descended upon the Apostles and they went forth to prophesy and proselytise to the peoples of the Earth. The rest, as they say, is history.

            Such is the Gospels’ account.

Christology. The traditional Christian perspective on Jesus is governed by several doctrines. First there is the doctrine of the Trinity. Jesus is one person of the Trinity; He is God the Son. Then there is the doctrine of the Hypostatic Union. This is a doctrine of the Incarnation, describing what happened when God became Flesh as Jesus. Famously even more technical and counterintuitive than the Trinity, the Hypostatic Union describes the nature of Christ while incarnate as ‘fully God and fully Man’, two natures (hypostases) existing in one person (united). This is the traditional doctrine of the Incarnation and along with the Trinity one of the most basic doctrines of mainstream Christianity.

The Atonement. When Jesus died on the cross, His sacrifice obviated human sin and enabled Him to accept souls for Heaven. How exactly this sacrifice worked and what if anything humans need to do to take advantage of it are two of the great still-debated questions in Christian theology.

Mariology. In the Catholic, Eastern Orthodox, and some Anglican churches, belief in the Virgin Mary is strong and she is venerated not just as a saint, but as the Mother of God and Queen of Heaven. Protestants, especially conservative Protestants, tend to look askance at the Marian tradition—partly because it further complicates the already uncomfortably pluriform Christian divine metric in the direction of polytheism, partly because it makes patriarchal societies like those in which conservative Protestantism flourishes a mite uncomfortable to have a woman so far up the ladder of divinity. Hence one might hear the canard that, on account of praying to Mary and the saints, Catholics worship them and are thus pagans. This is not true. Most religions in the world take the pragmatic line that if one wants to have something heard (like a prayer, for instance), one should logically tell it to as many people as will listen, even if most of them can’t do anything about it and especially if they can (and Mary, being God’s mamma and all, will make damn sure He listens). There’s a difference between worshipping someone/thing and telling it your problems in hopes that it can get something done.

            Roman Catholics do not worship Mary.

Sacraments. A sacrament is defined as a Christian ritual in which God is thought to be uniquely active.

Baptism. Baptism is the sacrament, with the use of water, by which one is admitted to membership of the Christian Church. Baptism was seen as in some sense necessary for salvation, until Huldrych Zwingli in the sixteenth century denied its necessity. Many denominations still maintain its necessity, however.

Eucharist. Eucharist, also known as Communion or the Lord’s Supper, is generally considered to be a commemoration of the Last Supper, the final meal that Jesus Christ shared with his disciples before his arrest and eventual crucifixion. Bread and wine, symbols of the body and blood of Christ, are consecrated and consumed by the celebrants. Like baptism, receiving the Eucharist has traditionally been considered necessary for salvation.

Other sacraments. The Roman Catholic Church and some other churches add an additional five sacraments to the above two: confirmation, holy orders or ordination, confession of sins, marriage, and anointing of the sick or extreme unction. Unlike baptism and the Eucharist, none of these are considered absolute necessities for salvation even by conservative Catholic theologians, though they are all thought to be preferable to the alternative (namely, not doing them). Marriage and holy orders are in the Roman Catholic Church mutually exclusive and left up to individual choice; many Christians are never married or ordained.