The only true source of light is Christ whose truth is given through inspiration from the Holy Ghost, which "will show unto [us] all things what [we] should do" (2 Nephi 32:5). We can know that we are safe from the practice of priestcraft when we earnestly encourage our listeners to determine for themselves the truth of what we teach, in accordance with the command to "prove all things" (1 Thes 5:21). As Nephi puts it, "Cursed is he that putteth his trust in man ... save their precepts shall be given by the power of the Holy Ghost" (2 Nephi 28:31).
An instructive example is given when the Lord commands us to let "our" light shine before the world (Matthew 5:16). The Book of Mormon provides important clarification to this teaching when it states that the light that we are to hold up is Christ himself (3 Nephi 18:24). He is our one and only Light (see John 1:1-9).
And though to preach or teach for gain might usually be associated with monetary gain, that gain might also be things such as respect, renown, popularity, or favors that motivate the teacher. Whenever a person receives gain for his service as a religious leader, he is in difficult territory, for it can compromise his humility and standing as a true servant of God. Of course, there are those who preach only for gain and don't care about their standing before the Lord.
That The Church of Jesus Christ of Latter-day Saints has a lay clergy helps to avoid priestcraft, at least in the form of monetary gain. The great majority who minister in the work of the Church serve in callings that are temporary. Missionaries, too, are relocated within their missions often to keep them from building a following among the people they teach. Even within a calling, humility is important:
- Those who engage in self-congratulation over a supposed strength have lost the protection of humility and are vulnerable to Satan’s using that strength to produce their downfall. In contrast, if we are humble and teachable, hearkening to the commandments of God, the counsel of his leaders, and the promptings of his Spirit, we can be guided in how to use our spiritual gifts, our accomplishments, and all of our other strengths for righteousness. And we can be guided in how to avoid Satan’s efforts to use our strengths to cause our downfall. 
- Charismatic teachers [within the Church can become engaged in priestcraft]. With a trained mind and a skillful manner of presentation, teachers can become unusually popular and effective in teaching. But Satan will try to use that strength to corrupt teachers by encouraging them to gather a following of disciples. A Church teacher, Church Education System instructor, or Latter-day Saint university professor who gathers such a following and does this “for the sake of riches and honor” (Alma 1:16) is guilty of priestcraft. “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).
- Teachers who are most popular, and therefore most effective, have a special susceptibility to priestcraft. If they are not careful, their strength can become their spiritual downfall. They can become like Almon Babbitt, with whom the Lord was not pleased, because “he aspireth to establish his counsel instead of the counsel which I have ordained, even that of the Presidency of my Church; and he setteth up a golden calf for the worship of my people” (Doctrine and Covenants 124:84).
- He criticized the Church and taught that priests and teachers should become popular with the people (see Alma 1:3). This shows us that he wanted the people to praise and follow him rather than God.
- He taught that all priests and teachers (like himself) should be paid for preaching rather than also working to support themselves (see v. 3). This shows that his desire was to get gain and prosper from the labor of others.
- In order to get paid for preaching, Nehor, like all false teachers, taught what the people wanted to hear. He taught that “all mankind should be saved at the last day” (v. 4). That doctrine would be very pleasing to the disobedient. How much easier and comforting it is to hear that everyone will be saved instead of being taught that such principles as faith, repentance, and obedience are necessary for salvation. This shows that Nehor was more interested in his own welfare than in helping the people grow in righteousness and in the welfare of Zion. 
"Service that is ostensibly unselfish but is really for the sake of riches or honor surely comes within the Savior’s condemnation of those who 'outwardly appear righteous unto men, but within … are full of hypocrisy and iniquity' (Matthew 23:28). Such service earns no gospel reward.
“'I would that ye should do alms unto the poor,' the Savior declared, 'but take heed that ye do not your alms before men to be seen of them; otherwise ye have no reward of your Father who is in heaven' (3 Nephi 13:1; see also Matthew 6:1–2). The Savior continued:
“'Therefore, when ye shall do your alms do not sound a trumpet before you, as will hypocrites do in the synagogues and in the streets, that they may have glory of men. Verily I say unto you, they have their reward' (3 Nephi 13:2; see also Matthew 6:2).
"In contrast, those who serve quietly, even 'in secret,' qualify for the Savior’s promise that 'thy Father, who seeth in secret, shall reward thee openly' (3 Nephi 13:18; see also Matthew 6:4). 
- See also 2 Nephi 4:34.
- Dallin H. Oaks, “Our Strengths Can Become Our Downfall,” Ensign, Oct 1994, 11.
- Book of Mormon seminary manual:Alma
- Dallin H. Oaks, “Why Do We Serve?,” Ensign, Nov 1984, 12.