Why was a restoration of the gospel necessary? What is the real/true message of the restoration? How many restorations from apostasy have occurred?
Whenever the gospel is taken from the earth such that no valid priesthood authority remains, the gospel must be restored by heavenly messengers to restore priesthood authority to the earth and to reintroduce the principles and the saving ordinances of the gospel. All of the dispensations of the gospel, from Adam to Jesus Christ, have been lost through apostasy. Only the dispensation of the fulness of times–restored through the Prophet Joseph Smith–has been promised not to end in apostasy, but to eventually fill the whole earth, as prophesied by Daniel—
And in the days of these kings shall the God of heaven set up a kingdom, which shall never be destroyed: and the kingdom shall not be left to other people, but it shall break in pieces and consume all these kingdoms, and it shall stand for ever (Dan 2:44).
The apostasy that occurred following the mortal ministry of the Savior was on this wise. The Church had been established with apostles, prophets, evangelists, pastors, teachers and so forth (see Eph 4:11-12). Peter, James and John were called and functioned as the First Presidency of the Church. However, before the Church could be fully established, all the apostles save John, who was banished to the Isle of Patmos, were put to death. So the general priesthood authority of the Church was lost. All that remained were the local authorities, i.e., the bishops who presided over the local units of the Church. The bishops had no jurisdictional authority outside of their own units. They had authority to function only in the Aaronic priesthood. With the general authorities gone, no new bishops could be ordained. So when the last bishop who had been ordained by one of the apostles died, the last vestige of priesthood authority perished with him, and the apostasy was complete
With the gospel taken from the earth the dark ages followed. Without continued revelation from heaven the earth sank into a great abyss of ignorance and sin. When the time was right, the Lord inspired great and valiant men to begin enlightening the world to establish an environment in which revealed truth could flourish. President Boyd K. Packer of the Council of the Twelve of The Church of Jesus Christ of Latter-day Saints recorded—
“We owe an immense debt to the protesters and the reformers who preserved the scriptures and translated them. They knew something had been lost. They kept the flame alive as best they could. Many of them were martyrs. But protesting was not enough; nor could reformers restore that which was gone” (President Boyd K. Packer, The Cloven Tongues of Fire, Ensign, May 2000, p.7)
There was also an intellectual enlightenment that was sparked by the invention of the printing press. The dogma of the Catholic Church was finally successfully countered by the religious reformers starting with Martin Luther.
The discovery of America and its subsequent colonization by those who had flown civil and religious persecution in England and other European countries, resulted in the development of a governmental constitution that guaranteed the freedom of speech, the freedom of the press, the right to own property, etc. This unique constitution was crafted in such a way that for the first time in history all implied powers rested with the people rather than with the government–the government having no power except that which was expressly given to it by the people.
All of these developments were inspired by God for the specific purpose of preparing a climate in which the kingdom of God could be restored to the earth and not be overcome by evil men bent on destroying the work of God.
So on a spring morning in 1820 in one of the most marvelous visions of all time God the Father and His Son Jesus Christ appeared to a young lad only 14 years of age by the name of Joseph Smith and commissioned him to usher in the dispensation of the fullness of times. In a subsequent revelation to Joseph Smith in October of 1831, it states—
The keys of the kingdom of God are committed unto man on the earth, and from thence shall the gospel roll forth unto the ends of the earth, as the stone which is cut out of the mountain without hands shall roll forth, until it has filled the whole earth (D&C 65:2)
This stone, as mentioned above, is that which was referred to by Daniel in his interpretation of King Nabuchanezzar’s dream. (Daniel 2:44)