"Yea, and many did preach with exceedingly great power and authority, unto the bringing down many of them into the depths of humility, to be the humble followers of God and the Lamb."
New converts to the Church always seem to have an inner fire when it comes to sharing the Gospel with others. I've seen that same drive in primary children and youth. So what happens to those of us born into the Church? Where is our urge to share our precious knowledge with others? Did we have it as children, and then lose it as we grew up? What is it that changes within us?
I think the answer is charity. As children, we hadn't yet learned that people can be cruel. We trusted everyone, played with anyone. But as we grew, we learned that some people weren't worthy of our trust. We began to approach everyone with distrust. So we lost our desire to be in the celestial kingdom with everyone, and really only wanted to be there with the ones we love and care about.
However, when we begin to feel Christ-like love for those around us, we overcome those feelings of distrust, and feel again a desire to share the gospel. We can pray for missionary experiences and opportunities all we want, but until we truly care about the people we meet or associate with, we give the Lord very little to work with.
The converted Lamanites mentioned in Helaman loved their brethren the Nephites with the love of Christ. It brought them from the land of Nephi to the land of Zarahemla, a long journey, to share their conversion stories and preach the gospel. They could have said, "The'll never change. They've become too wicked." But they didn't judge; they only loved. And in doing so, brought many Nephites back to the fold.