Obviously if God needs to restore things that were lost that were previously revealed, then there must have been some type of falling away from those things or apostacy. One of the things that I believe needed to be restored was the Holy Apostleship. After most of the apostles of Jesus' day were murdered, we don't hear of any apostles after that. Yet the apostles were known as part of the foundation of the church:
Ephesians 2:19-20
19 Now therefore ye are no more strangers and foreigners, but fellowcitizens with the saints, and of the household of God;
20 And are built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief corner stone;
and from the Apostle Paul we read:
Ephesians 4:11-15
11 And he gave some, apostles; and some, prophets; and some, evangelists; and some, pastors and teachers;
12 For the perfecting of the saints, for the work of the ministry, for the edifying of the body of Christ:
13 Till we all come in the unity of the faith, and of the knowledge of the Son of God, unto a perfect man, unto the measure of the stature of the fulness of Christ:
14 That we henceforth be no more children, tossed to and fro, and carried about with every wind of doctrine, by the sleight of men, and cunning craftiness, whereby they lie in wait to deceive;
15 But speaking the truth in love, may grow up into him in all things, which is the head, even Christ:
In these verses we read that apostles and prophets were a part of the foundation of the church and that we were to have apostles and prophets until we all came to the unity of the faith, and of the knowledge of the Son of God, unto a perfect man, unto the measure of the stature of the fulness of Christ. We all know that we have not reached that point and thus we should still have apostles and prophets in the church.
When was the last time we saw apostles and prophets in the catholic church? During the reformation, the protestants had no apostles or prophets and turned to "Sola Scriptura" as their authority. But if we were to always have apostles and prophets in the church until we all came to the unity of the faith as spoken of above, we would have continuing revelation and prophesy in the church. Ezekiel 37 speaks of receiving additional scripture beyond the Bible (stick of Judah) which would be known as the stick of Joseph or Ephraim. So I think through apostacy from Christ's original church, there came a need to have restitution of the church along with apostles and prophets. The restitution of all things began back in 1820 when Jesus again appeared to the prophet Joseph Smith and by 1830 restored his church again on this earth with apostles and prophets. This restitution will continue up until the second coming of our Lord and Savior Jesus Christ. It will then continue on throughout the Millennial era but we will have Jesus in our midst to lead his people for a thousand years.