Jesus Christ bestowed priesthood authority upon the 12, while he was on earth to teach true doctrine in His and received revelation (scripture). As the apostles died, priesthood authority also died on the earth. This means revelation ceased. Either by innocent mistake or devious design, essential doctrines were lost or corrupted.
"Behold, the days come, saith the Lord God, that I will send a famine in the land, not a famine of bread, nor a thirst for water, but of hearing the words of the Lord: And they shall wander from sea to sea, and from the north even to the east, they shall run to and fro to seek the word of the Lord, and shall not find it." Amos 8:11-12
"Let no man deceive you by any means: afor that day shall not come, except there come a falling away first, and that man of sin be revealed, the son of perdition;" 2 Thessalonians 2:3
This apostasy and restoration was prophesied of by Isaiah. "Wherefore the Lord said, Forasmuch as this people draw near me with their mouth, and with their lips do honor me, but have removed their heart far from me, and their fear toward me is taught by the precept of men: Therefore, behold, I will proceed to do a marvelous work among this people, even a marvelous work and a wonder: for the wisdom of their wise men shall perish, and the understanding of their prudent men shall be hid." Isaiah 29:13-4
Jesus Christ restored His church through the modern-day prophet, Joseph Smith. "Wherefore, I the Lord, knowing the calamity which should come upon the inhabitants of the earth, called upon my servant Joseph Smith, Jun., and spake unto him from heaven, and gave him commandments; And also gave commandments to others, that they should proclaim these things unto the world; and all this that it might be fulfilled, which was written by the prophets—The weak things of the world shall come forth and break down the mighty and strong ones, that man should not counsel his fellow man, neither trust in the arm of flesh—But that every man might speak in the name of God the Lord, even the Savior of the world; That faith also might increase in the earth; That mine everlasting covenant might be established; That the fulness of my gospel might be proclaimed by the weak and the simple unto the ends of the world, and before kings and rulers. And also those to whom these commandments were given, might have power to lay the foundation of this church, and to bring it forth out of obscurity and out of darkness, the only true and living church upon the face of the whole earth, with which I, the Lord, am well pleased, speaking unto the church collectively and not individually—" Doctrine and Covenants 1:17-23&30