Why Does The Church of Jesus Christ of Latter-day Saints Send Out Missionaries?

https://www.lds.org/media-library/video/2013-02-2000-mormon-missionaries?category=missionary/introduction-to-mormons&lang=eng

I've heard that some people say that members of The Church of Jesus Christ of Latter-day Saints send their young men out on missions because it is a "rite of passage". Obviously, they haven't been around many young men. I've not yet met any young man who would give up his job, car, music, cell phone, and laptop, leave his girlfriend, and postpone his college plans, so he could travel to a strange place where he would have doors slammed in his face all day, just for a "rite of passage". 

Did Joseph Smith Start The Church of Jesus Christ of Latter-day Saints?

https://www.mormon.org/beliefs/jesus-christs-church

Members of The Church of Jesus Christ of Latter-day Saints, find that an odd question. It is like asking if Moses made up the Ten Commandments. Moses was a prophet. Prophets listen to what God has to say, then they teach it to the people. They have the assignment to help the rest of us learn how to be happy and know what we need to do to return to our Heavenly Father someday. 

Aware of our weaknesses, God has always used Prophets to help us learn and grow. The Old Testament contains the record of God's dealings with man through His prophets. In the New Testament, Jesus Christ set up His Church, gave His Apostles priesthood authority, and designated Peter to be the prophet who would continue to receive revelation for His church, The Church of Jesus Christ of Early-day Saints (saints just means a church member). (see Peter receiving revelation to take Gospel to Gentiles)