The term, priestcraft, is defined in 2 Nephi 26:29 as the practice in which men preach and set themselves up for a light unto the world, that they may get gain and praise of the world; but they seek not the welfare of Zion.
Dallin H. Oaks
"The Book of Mormon applies this principle (priestcraft) to those who seem to be serving the Lord but do so with a hidden motive to gain personal advantage rather than to further the work of the Lord: ’Priestcrafts are that men preach and set themselves up for a light unto the world, that they may get gain and praise of the world; but they seek not the welfare of Zion’ (2 Nephi 26:29; see also Alma 1:16).
"Priestcraft is the sin committed by the combination of a good act--such as preaching or teaching the gospel--and a bad motive. The act may be good and visible, but the sin is in the motive. On earth, the wrong motive may be known only to the actor, but in heaven it is always known to God.
“…During my lifetime, I have seen more than a few persons in positions of responsibility in various churches whose activities in the ‘work of the Lord’ seemed to be motivated predominantly by personal interest. The commandment to avoid priestcraft is a vital challenge to religious persons in every age of time.” (Pure in Heart, pp. 16-18)
Bruce R. McConkie
"Priesthood and priestcraft are two opposites; one is of God, the other of the devil. When ministers claim but do not possess the priesthood; when they set themselves up as lights to their congregations, but do not preach the pure and full gospel; when their interest is in gaining personal popularity and financial gain, rather than in caring for the poor and ministering to the wants and needs of their fellow men -- they are engaged, in a greater or lesser degree, in the practice of priestcrafts.
“Apostasy is born of priestcrafts (2 Ne. 10:5; 3 Ne. 16:10; D. & C. 33:4), for those who engage in them follow vain things, teach false doctrines, love riches, and aspire to personal honors. (Alma 1:12, 16.) Men are commanded to repent of their priestcrafts (3 Ne. 30:2), and eventually, in the millennial day, these great evils will be done away. (3 Ne. 21:19.)” (Mormon Doctrine, p. 593-4)
In a talk given to seminary and institute instructors, Robert Millet, a co-author of Doctrinal Commentary on the Book of Mormon stated:
“There is a difference between developing and enjoying the needed rapport with our students on the one hand, and developing a following on the other….We cannot always control how people feel toward us or what we teach, but we can strive to be certain that our own motives are pure. I cannot speak for anyone else, but I believe if I have begun to attract people to myself rather than to the Lord, that I need to undergo some serious introspection. My colleague Joseph McConkie observed to this group some years ago: ’Sometimes we get in our own way. We block the light because we are standing center stage when we should have stepped to the side and just let the [message] speak for itself. We cause what I call a spiritual eclipse.’ (CES Symposium, 8-82, p. 1). If I am driven more by ego than by a desire to lead people to Christ; if my desires for acclaim are greater than my desires to love and serve the Lord and his children, then my eye is not single to the glory of God (Matt. 6:22-23; D&C 88:67-68), and I will obstruct the light that might have been seen and felt. If, on the other hand, I am humbled to be in the presence of my students, sobered by the sacred assignment to instruct them, and fully cognizant of and willing to trust in Him who [is] the real Teacher and Converter, then I will have the privilege of witnessing miracles, men and women coming unto Christ and being perfected in him.” (CES Symposium, Aug. 1993, p. 11 as taken from Latter-day Commentary on the Book of Mormon compiled by K. Douglas Bassett, pp. 245-6)