This is part of a great discourse given by the prophet Alma to a people who did not believe in Jesus Christ. He likens this belief to a seed, and gives counsel on how to grow that belief.
Alma 32 27-43
27 But behold, if ye will awake and arouse your faculties, even to an experiment upon my words, and exercise a particle of faith, yea, even if ye can no more than desire to believe, let this desire work in you, even until ye believe in a manner that ye can give place for a portion of my words.
28 Now, we will compare the word unto a seed. Now, if ye give place, that a seed may be planted in your heart, behold, if it be a true seed, or a good seed, if ye do not cast it out by your unbelief, that ye will resist the Spirit of the Lord, behold, it will begin to swell within your breasts; and when you feel these swelling motions, ye will begin to say within yourselves—It must needs be that this is a good seed, or that the word is good, for it beginneth to enlarge my soul; yea, it beginneth to enlighten my understanding, yea, it beginneth to be delicious to me.
30 But behold, as the seed swelleth, and sprouteth, and beginneth to grow, then you must needs say that the seed is good; for behold it swelleth, and sprouteth, and beginneth to grow. And now, behold, will not this strengthen your faith? Yea, it will strengthen your faith: for ye will say I know that this is a good seed; for behold it sprouteth and beginneth to grow.
34 And now, behold, is your knowledge perfect? Yea, your knowledge is perfect in that thing, and your faith is dormant; and this because you know, for ye know that the word hath swelled your souls, and ye also know that it hath sprouted up, that your understanding doth begin to be enlightened, and your mind doth begin to expand.
42 And because of your diligence and your faith and your patience with the word in nourishing it, that it may take root in you, behold, by and by ye shall pluck the fruit thereof, which is most precious, which is sweet above all that is sweet, and which is white above all that is white, yea, and pure above all that is pure; and ye shall feast upon this fruit even until ye are filled, that ye hunger not, neither shall ye thirst.