Why Is LDS Missionary Work So Successful?

I just read a promise that was given by the Lord through his prophet, Joseph Smith, back in 1840 to a couple of missionaries. This same promise holds true for today's nearly 60,000 missionaries throughout the world. First I'll give the quote, and then I'll explain why I think it is important:

"Do not be discouraged on account of the greatness of the work; only be humble and faithful...He who scattered Israel has promised to gather them; therefore inasmuch as you are to be instrumental in this great work, He will endow you with power, wisdom, might, and intelligence, and every qualification necessary; while your minds will expand wider and wider, until you can circumscribe the earth and the heavens, reach forth into eternity, and contemplate the mighty acts of Jehovah in all their variety and glory."
- Joseph Smith, May 14, 1840

First of all, you must understand what missionary work is. The Church of Jesus Christ of Latter-day Saints is God's church on the earth, so it is doing His work. The same Jehovah that scattered Israel in Old Testament times, is now gathering Israel, just as he promised dozens of times throughout the Bible. This gathering is being done by our missionaries. The house of Israel are all those who convert to Christ's church and choose to gather to it.

This post's title phrases the question, "Why is LDS missionary work so successful?" Well an obvious answer is because it's God's work. This promise quoted above from Joseph Smith is more specific. The promise is that those who are instrumental in His great work [missionary work or the gather], will be endowed with "power, wisdom, might, and intelligence, and every qualification necessary." How can anyone fail with a promise like that from God's prophet?

Think about it. Mormon missionaries are almost all between the ages of 19 and 21. How much does a 19-year-old boy know? How influential and persuasive are 19-year-olds? How smart, intelligent, wise is a 19-year-old kid? Sometimes they think they know everything, but really they are weak. Paul was not far off at all when he said:

"But God hath chosen the foolish things of the world to confound the wise; and God hath chosen the weak things of the world to confound the things which are mighty;"
1 Corinthians 1:27

So, with this explanation, I hope it is a little more clear how our missionaries are so successful. They not only are on the Lord's errand, but they are also filled with his power. Feel free to see for yourself by inviting them to speak to you some time. You'll notice in just one visit that they are empowered from on high.