Great Apostasy

Mormonism teaches that not long after Jesus Christ's lifetime, internal rebellions within the early Christian community caused the primitive Christian Church, led by the Twelve Apostles to disappear and be replaced by many factions, each of which had pieces of the truth, but not a fullness. More importantly, this falling away (see 2 Thessalonians 2:3) resulted in a loss of authority, which Mormons call Priesthood. Without proper authority from God, man cannot perform the ordinances of the Church.
During Jesus' ministry, He established His Church. He called Apostles and Prophets and gave them authority to act in His name and teach the gospel. In Luke 6:12-16, it says—
:...and it came to pass in those days, that he went out into a mountain to pray, and continued all night in prayer to God. And when it was day, he called unto him his disciples: and of them he chose twelve, whom also he named apostles; Simon, (whom he also named Peter,) and Andrew his brother, James and John, Philip and Bartholomew, Matthew and Thomas, James the son of Alphaeus, and Simon called Zelotes, And Judas the brother of James, and Judas Iscariot, which also was the traitor.
It is important to understand that the priesthood is not a group of priests, but the authority to act in the name of God. 
After Jesus was crucified, the apostles and prophets He appointed continued to receive revelation for the Church. They recorded these things in the scriptures and taught them to the people. The apostles and prophets went into different lands to teach the gospel, but they were rejected. Even some of the members of the Christ's Church began to fall away from the teachings of the gospel. The New Testament documents the many inspired teachings of the early Apostles; it also documents the difficulties and challenges the early Church faced. Paul's epistles, especially, record many references to people within the Church teaching false doctrines, attempting to usurp power, or leading other's astray. Paul also mentions that some people were circulating false letters in the name of the Apostles.
Many of the Apostles and righteous members of Christ's Church were killed by the wicked, and the priesthood along with Christ's Church were taken from the earth. Persecution of those who were called Christians began in about the first century by the Roman Empire. Revelation could no longer be received on behalf of the Church, because there was no one authorized by God to receive it, although individuals could and continued to receive inspiration in their personal lives. Because men could not receive revelation and understanding from God, men began to rely on their own wisdom and traditions to interpret scriptures and Christ's teachings. This caused much confusion and false ideas about God, Jesus, and His Church. 
Fragments of Christ's Church were all that remained, and they often mixed with pagan practices or the practices of other religions. The world fell into apostasy, which means that the full truth of the gospel was not on the earth. Apostasy comes from the Greek word meaning rebellion. The more pervasive beliefs came to be viewed as more Orthodox. That is, ideas originating in large population areas carried more weight.1 As apostasy gradually grew, there was a need to codify Christian beliefs. 
:In the year a.d. 325 the Roman emperor Constantine convened the Council of Nicaea to address—among other things—the growing issue of God’s alleged “trinity in unity.” What emerged from the heated contentions of churchmen, philosophers, and ecclesiastical dignitaries came to be known (after another 125 years and three more major councils) as the Nicene Creed, with later reformulations such as the Athanasian Creed. These various evolutions and iterations of creeds—and others to come over the centuries—declared the Father, Son, and Holy Ghost to be abstract, absolute, transcendent, imminent, consubstantial, coeternal, and unknowable, without body, parts, or passions and dwelling outside space and time. In such creeds all three members are separate persons, but they are a single being, the oft-noted “mystery of the trinity.” They are three distinct persons, yet not three Gods but one. All three persons are incomprehensible, yet it is one God who is incomprehensible.2
:The formal doctrine of the Trinity as it was defined by the great church councils of the fourth and fifth centuries is not to be found in the [New Testament].3
Members of The Church of Jesus Christ of Latter-day Saints declare it is self-evident from the scriptures that the Father, the Son, and the Holy Ghost are separate persons, three divine beings, noting such unequivocal illustrations as the Savior's great Intercessory Prayer just mentioned, His baptism at the hands of John, the experience on the Mount of Transfiguration, and the martyrdom of Stephen—to name just four.4
Latter-day Saints uphold the glorious resurrection of Jesus Christ. According to the Nicaean and Anathasian Creeds, Christ would have of necessity shed His resurrected body to return to the spirit-entity called the Trinity. Latter-day Saints proclaim that resurrection is the desirable, eternal state, the state of both God the Father and Jesus Christ. If not, then why was Christ resurrected at all? Mormons find the Trinitarian beliefs of the fifth century incomprehensible, the inventions of men.
Over the centuries, God and Christ have continued to guide mankind towards a restoration of truth. During the reformation and enlightenment in Europe, brave men were willing to face martyrdom in order to reform the Orthodox Churches. Christopher Columbus was inspired of God to seek his route to the Orient. He found a "new" continent, where a land of religious freedom could be established, and true doctrine could be reintroduced. 
The Restoration, a necessary event after an apostasy, came about through Joseph Smith. In the spring of 1829, while translating the Book of Mormon, Joseph Smith and Oliver Cowdery were visited by heavenly messengers who restored to them the Priesthood, the authority to act in God's name. In 1830, the Church of Christ, as the Mormon Church was originally called, was organized officially. The authority to act in God's name was restored, as was true doctrine. Latter-day Saints believe there are again Apostles on the earth, and a Prophet who guides the Church of Christ through revelation and the power of the priesthood. 
==References==
*1 Bart D. Ehrman, The Orthodox Corruption of Scripture, Oxford University Press, U.S.A.
*2 Jeffrey R. Holland, “The Only True God and Jesus Christ Whom He Hath Sent,” Liahona, Nov 2007, 40–42.
*3 Harper’s Bible Dictionary, Paul F. Achtemeier, ed. (1985), p. 1099.
*4 Jeffrey R. Holland, “The Only True God and Jesus Christ Whom He Hath Sent,” Liahona, Nov 2007, 40–42.
==Links==
*FAIR LDS contains many articles on different aspects of the Great Apostasy.
*The Great Apostasy
*Video lecture:The Apostasy
*FAIRlds:How rejection of Church leaders led to the Great Apostasy
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