Alma 57 and 58 give us the amazing story of a band of just over two thousand young warriors who fought in several crucial battles for their people, the Nephites. Because of their courage and their faith, God kept every single on of them alive through the fighting, and gave them success in their attempts to defend their people from the attacks of the Lamanites.
They were unstoppable forces.
The stripling warriors, as they are often called, of the Ammonites, who joined the Nephite armies, had the same magical mixture of obedience, courage and faith as Captain Moroni, who was leading other armies on their side in the same war.
One key to success in missionary work, in spreading the Gospel of Jesus Christ, is to insist on refusing to doubt, to insist on keeping a hopeful, obedient point of view, to insist on fighting most desperately with a steely resolve to conquer.
And with that, to go forth with all your might.
See Alma 58:9-13. That passage will give you great strength and comfort in your trials, and help you fight harder and stronger to work as a valiant missionary.