Alma 17 - 19

Alma taught -

"...It is given unto many to know the mysteries of God; nevertheless they are laid under a strict command that they shall not impart only according to the portion of his word which he doth grant unto the children of men, according to the heed and diligence which they give unto him.
... and he that will not harden his heart, to him is given the greater portion of the word, until it is given unto him to know the mysteries of God until he know them in full." (Book of Mormon Alma 12:9 - 10)

As Alma met his friends, the sons of Mosiah on the road to the land of Gideon, he discovered that they -

"...had waxed strong in the knowledge of the truth; for they were men of a sound understanding and they had searched the scriptures diligently, that they might know the word of God.
3 But this is not all; they had given themselves to much prayer, and fasting; therefore they had the spirit of prophecy, and the spirit of revelation..." (Book of Mormon Alma 17:2 - 3)

And also that -

"...they fasted much and prayed much that the Lord would grant unto them a portion of his Spirit to go with them, and abide with them, that they might be an instrument in the hands of God to bring, if it were possible, their brethren, the Lamanites, to the knowledge of the truth..." (Book of Mormon Alma 17:9)

As Ammon, one of the sons of Mosiah on a mission to the lamanites, stood before King Lamoni, he tells him -

"..I am called by his Holy Spirit to teach these things unto this people, that they may be brought to a knowledge of that which is just and true;
35 And a portion of that Spirit dwelleth in me, which giveth me knowledge, and also power according to my faith and desires which are in God." (Book of Mormon Alma 18:34 - 35)

As King Lamoni begins to ask questions, Ammon asks -

"...Wilt thou hearken unto my words, if I tell thee by what power I do these things?..."
(Book of Mormon Alma 18:22)

King Lamoni responds -

"...Yea, I will believe all thy words..." (Book of Mormon Alma 18:23)

It is then that Ammon laid before him and his servants the scriptures and among other things -

"...he expounded unto them the plan of redemption, which was prepared from the foundation of the world; and he also made known unto them concerning the coming of Christ, and all the works of the Lord did he make known unto them." (Book of Mormon Alma 18:39)

And the King did not harden his heart but -

"...believed all his words." (Book of Mormon Alma 18:40)

For -

"...he began to cry unto the Lord, saying: O Lord, have mercy; according to thy abundant mercy which thou hast had upon the people of Nephi, have upon me, and my people.
42 And now, when he had said this, he fell unto the earth, as if he were dead." (Book of Mormon Alma 18:41 - 42)

And as promised by the Lord, the mysteries of God began to be unfolded to him, for Ammon recognized -

"...that the dark veil of unbelief was being cast away from his mind, and the light which did light up his mind, which was the light of the glory of God, which was a marvelous light of his goodness—yea, this light had infused such joy into his soul, the cloud of darkness having been dispelled, and that the light of everlasting life was lit up in his soul, yea, he knew that this had overcome his natural frame, and he was carried away in God—" (Book of Mormon Alma 19:6)

And two days later the King arose and testified -

"...behold, I have seen my Redeemer; and he shall come forth, and be born of a woman, and he shall redeem all mankind who believe on his name. " (Book of Mormon Alma 19:13)

And from time and afterward he began to teach -

"...the words which he had heard from the mouth of Ammon; and as many as heard his words believed, and were converted unto the Lord.

And the King, Ammon, and his converted servants -

"...did all declare unto the people the selfsame thing—that their hearts had been changed; that they had no more desire to do evil." (Book of Mormon Alma 19:31 - 33)

"...thus the Lord did begin to pour out his Spirit upon them; and we see that his arm is extended to all people who will repent and believe on his name." (Book of Mormon Alma 19:36)

"...For he that diligently seeketh shall find; and the mysteries of God shall be unfolded unto them, by the power of the Holy Ghost..." (Book of Mormon 1 Nephi 10:19)