Doctrine & Covenants 79-81
Advice for missionaries (and all of us):
Proclaim glad tidings of great joy.
The Comforter teaches truth and shows us the way to go.
Let your heart be glad.
Succor the weak; lift up the hands which hang down, strengthen the feeble knees.
Promote the glory of God.
And then the blessing that comes from obedience: "And if thou art faithful unto the end thou shalt have a crown of immortality, and aeternal life in the mansions which I have prepared in the house of my Father."