Alma 17

As the sons of Mosiah embarked on their mission to the Lamanites and journeyed in the wilderness -

"...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, to the knowledge of the baseness of the traditions of their fathers, which were not correct." (Book of Mormon Alma 17:9)

As Lamoni expressed a desire to believe in the words of Ammon, one of the sons of Mosiah, Ammon 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)

We begin to understand what it takes to receive this "portion of that Spirit" as Mormon writes -

"...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, and when they taught, they taught with power and authority of God." (Book of Mormon Alma 17:2 - 3)

These great missionaries had received knowledge, power, and increased faith as they diligently searched the scriptures with much prayer and fasting. And with that they had to show faith and patience as we are told -

"...they had many afflictions; they did suffer much, both in body and in mind, such as hunger, thirst and fatigue, and also much labor in the spirit." (Book of Mormon Alma 17:5)

This is how priesthood leaders are to prepare and magnify their callings.