A missionary's purpose is to bring souls to Christ.

2 Nephi 31:17-21

17 Wherefore, do the things which I have told you I have seen that your Lord and your Redeemer should do; for, for this cause have they been shown unto me, that ye might know the gate by which ye should enter. For the gate by which ye should enter is repentance and ^abaptism by water; and then cometh a remission of your sins by fire and by the Holy Ghost.

 18 And then are ye in this ^astrait and narrow ^bpath which leads to 

eternal life; yea, ye have entered in by the gate; ye have done according to the commandments of the Father and the Son; and ye have received the Holy Ghost, which ^cwitnesses of the ^dFatherand the Son, unto the fulfilling of the promise which he hath made, that if ye entered in by the way ye should receive.

 19 And now, my beloved brethren, after ye have gotten into this strait and narrow ^apath, I would ask if all is ^bdone? Behold, I say unto you, Nay; for ye have not come thus far save it were by the word of Christ with unshaken ^cfaith in him, ^drelying wholly upon the merits of him who is mighty to ^esave.

 20 Wherefore, ye must press forward with a ^asteadfastness in Christ, having a perfect brightness of ^bhope, and a ^clove of God and of all men. Wherefore, if ye shall press forward, feasting upon the word of Christ, and ^dendure to the end, behold, thus saith the Father: Ye shall have ^eeternal life.

 21 And now, behold, my beloved brethren, this is the ^away; and there is ^bnone other way nor ^cname given under heaven whereby man can be saved in the kingdom of God. And now, behold, this is the ^ddoctrine of Christ, and the only and true doctrine of the^eFather, and of the Son, and of the Holy Ghost, which is ^fone God, without end. Amen.