"I am the way, the truth and the life" (John 14:6) Christ told his followers during his brief but powerful ministry on earth. It was a timely and needed message since a few hundred years before His birth many people had stopped living according to God’s commandments. Christ brought light back into the world when He proclaimed His gospel just as he had to the prophets of old like Abraham, Isaac, and Moses. He chose twelve men to be His apostles—including Peter, James and John—and laid His hands on their heads to give them authority called the priesthood to perform baptisms, govern His church, and spread His word throughout the world.
In spite of His great influence and many miracles, He was ultimately rejected and crucified. After his death, His brave and faithful apostles carried on without Him, baptizing new members, and starting various congregations.
The Dark Ages of Christianity
Regardless of the valiant efforts of Christ’s apostles and their faithful followers, the original church that Christ restored began to fade away. Members faced severe persecution and all but one of the apostles were martyred. This is a period called the Great Apostasy, when there was a "falling away" (2 Thessalonians 2:1-3) from the gospel Christ organized. The apostolic authority to bestow priesthood keys and to receive revelation for the Church was lost along with many precious teachings. Errors about His teachings crept into the church resulting in conflicting opinions and lost truths. This period is what we call the Great Apostasy.
Without authority or divine direction, Christianity struggled to survive with conflicting opinions on even the most basic teachings of the gospel. Without priesthood authority or the full gospel, people had to rely on human wisdom to interpret the scriptures, principles and ordinances. Many false ideas were taught as truth, and much of what we know about the true character and nature of God the Father, His Son Jesus Christ, and the Holy Ghost was lost. Essential doctrines like faith, repentance, baptism, and the gift of the Holy Ghost became distorted and important doctrines were lost entirely.
Centuries later, inspired people, such as Martin Luther and John Calvin, recognized that practices and doctrines had been changed or lost and tried to reform the churches to which they belonged. But without the authority of the apostles of the Lord Jesus Christ, His gospel and Church could not be returned to their original form.