D&C 19:29 And thou shalt adeclare glad tidings, yea, bpublish it upon the mountains, and upon every high place, and among every people that thou shalt be permitted to see.
31 And of atenets thou shalt not talk, but thou shalt declare repentance and bfaith on the Savior, and cremission of sins by dbaptism, and by efire, yea, even the fHoly Ghost.
This is the mandate for a missionary, to declare glad tidings. Some zealots have got it wrong and thought their job was to frighten people with death and fire and destruction and brimstone.
The scripture does say to declare repentance, but I think that when we teach faith in the Savior first, as the 4th Article of Faith orders them, that the other things fall into place. If we truly have faith in Him and understand true principles, we automatically want to be clean before Him. If we love Him, we want to have Him in our lives, but we are embarrassed and grieved to have Him see our sins, so we work to repent of them.
So I would say that we need to declare the glad tidings of Christ - His love for us, His sacrifice for us, the glad tidings of His Atonement. And the scripture says to do it with humility, trusting in Him. Proud missionaries do more damage than good, because pride is an enmity towards God and our fellowmen. We must love those we teach, have humility, and trust Him and the Spirit to do the actual teaching.
Alicia Arce told us a story in Relief Society about teaching her little granddaughter about Jesus. The child isn't getting any religious teaching in their home, so Alicia decided it was up to her to share her love for the Savior with the child. She must have done a good job, because when Oscar came home, Alicia told the girl, "Tell Grandpa about Jesus." And the little girl said, "Me and Grandma are crazy about that Guy!"
If we are crazy about that Guy, we'll want to share His glad tidings and bless those around us to know Him and love Him too. That's what missionaries do.
