Surely the Lord God does nothing unless He reveals His secret to His servants the prophets.Amos 3:7
I've been thinking a lot about prophets lately. The belief that God continues to speak to humankind through prophets just as He did in old times is one of the beliefs that sets Latter-day Saints apart from the rest of Christianity.
When I was on my mission (in Charlotte, North Carolina), the first lesson we always taught was about how God has called prophets since the beginning of time to preach His word. We would explain that God would call a prophet to preach, the people would listen and repent, and after a while (sometimes a short time, sometimes several generations), the people would fall away. Time would pass and then God would call a new prophet. This cycle has repeated throughout human history.
Generally, this portion of the message was well-received as I went through a list of Old Testament prophets. Once I hit New Testament times, people were less convinced. By the time I explained that God still calls prophets today, few people believed what I was telling them. They said that after Jesus came, prophets were no longer necessary.
It always struck me as completely logical that since God spoke to His people in ancient times that He would speak to people today, too. That logic has led me down some interesting thought paths lately.
The church teaches of the great apostasy - the period of time from after the death of the apostles in approximately 100 AD until Joseph Smith was called as a prophet in 1820. (Technically, I think starting the apostasy at 400 AD is more accurate, since Moroni was still around until then.) With God's pattern of constantly calling prophets, why did He wait nearly 1400 years before calling another one?
Maybe He didn't. In that gap between Moroni and Joseph Smith, a lot of people lived. What if God called prophets in that time? There's precedent for people rejecting the messages of prophets, so maybe people just didn't accept what they were hearing. There's also precedent for people accepting the message but then the message getting corrupted in transmission.  When the whole course of human history is revealed, it would not surprise me in the slightest to find that there were failed attempts at restoring the gospel before 1820.
 Most of the New Testament is directed at this very problem. Paul wrote many letters trying to correct the errors that were creeping into the church.