2 Nephi 28

The mutual theme this year is -

"Wherefore, ye must press forward with a steadfastness in Christ, having a perfect brightness of hope, and a love of God and of all men. Wherefore, if ye shall press forward, feasting upon the word of Christ, and endure to the end, behold, thus saith the Father: Ye shall have eternal life."  (Book of Mormon | 2 Nephi 31:20)

As Nephi explains with plainness the word of Christ, he teaches -

"Wo be unto him that shall say: We have received the word of God, and we need no more of the word of God, for we have enough!
30 For behold, thus saith the Lord God: I will give unto the children of men line upon line, precept upon precept, here a little and there a little; and blessed are those who hearken unto my precepts, and lend an ear unto my counsel, for they shall learn wisdom; for unto him that receiveth I will give more; and from them that shall say, We have enough, from them shall be taken away even that which they have."  (Book of Mormon | 2 Nephi 28:29 - 30)

Thus the reason we are counseled to feast upon the word of Christ is to continue to learn little by little which provides great assurance and knowledge.  We also learn that those that think they have enough, that which they have been given will be taken away.