D & C 1:38 is frequently proof-texted in common Mormon usage.

Let’s begin with the text, which is part of the introduction to the Doctrine and Covenants; I have bolded the part which is often removed from its context:

Search these commandments, for they are true and faithful, and the prophecies and promises which are in them shall all be fulfilled. What I the Lord have spoken, I have spoken, and I excuse not myself; and though the heavens and the earth pass away, my word shall not pass away, but shall all be fulfilled, whether by mine own voice or by the voice of my servants, it is the same. (D & C 1:37-38)

Here’s what these verses mean in context: what the Lord has spoken will come to pass, whether it came directly from him or whether it came through one of his servants. These verses have absolutely nothing to say about whether everything a servant of the Lord ever speaks is “the same” as what the Lord himself would speak. Frequently in the church, speakers will yank the bolded part out of context in order to suggest that anything a servant of the Lord speaks is “the same” as what the Lord would speak with his own voice. But these two verses simply do not support that reading: the topic here is not the reliability of the Lord’s servants; rather, the topic is the fulfillment of the Lord’s words and the point is that they will be fulfilled whether they come directly from him or through a servant. Again, a crucial point: these verses have nothing to say about whether everything a servant of the Lord speaks reflects what the Lord would speak. However, the rest of the passage does have something to say about that topic. Earlier, the Lord said this:

these commandments are of me, and were given unto my servants in their weakness, after the manner of their language, that they might come to understanding. And inasmuch as they erred it might be made known; And inasmuch as they sought wisdom they might be instructed; And inasmuch as they sinned they might be chastened, that they might repent; And inasmuch as they were humble they might be made strong, and blessed from on high, and receive knowledge from time to time. (D & C 1:24-28)

Notice that we are talking about the servants of the Lord again. And what does the Lord have to say about his servants? That they are weak. That the commandments are not presented as some platonic ideal but rather “after the manner of their language.” That the servants have erred(!). That they have sinned(!). This is really important context for D & C 1:38, especially coming just a handful of verses before that passage: it suggests that the servants of the Lord are weak, limited by their language, will sin, and will err. Now, that’s no excuse for not listening to them (something the section encourages), but there is absolutely no warrant in this section for thinking that anything a servant of the Lord says is precisely the same as what the Lord would say. Rather, 1:24-28 imply precisely the opposite.

Let me also suggest that the use of the word “servants” in 1:38 should have been the first clue that using 1:38 to preach prophetic infallability was a bad idea. Verse 20 suggests that the term “servants” applies to everyone who wants to be one. Verse 14 makes clear that “servants” is not a synonym for “prophets and apostles.” Verse 18 does this as well, by mentioning “others” in addition to Joseph Smith; verse 30 repeats it again. And verse 30 also makes clear that while the Lord is well pleased with the church collectively, that does not mean that he is perfectly pleased with any individual.

The misuse of this text to imply prophetic inerrancy is not just bad because it is inaccurate; it is bad because it creates false expectations of what a prophet is and does. That false impression of prophetic perfection often leads to a crisis of faith when a person realizes that prophets have indeed made mistakes. In contrast with this misleading reading of D & C 1:38, our leaders have actually been trying to teach about prophetic errancy recently:

President Dieter F. Uchtdorf: “And, to be perfectly frank, there have been times when members or leaders in the Church have simply made mistakes. There may have been things said or done that were not in harmony with our values, principles, or doctrine. I suppose the Church would be perfect only if it were run by perfect beings. God is perfect, and His doctrine is pure. But He works through us—His imperfect children—and imperfect people make mistakes” (citation).

Elder Jeffrey R. Holland: “So be kind regarding human frailty—your own as well as that of those who serve with you in a Church led by volunteer, mortal men and women. Except in the case of His only perfect Begotten Son, imperfect people are all God has ever had to work with. That must be terribly frustrating to Him, but He deals with it. So should we.” (citation).

Elder M. Russell Ballard: “The Church of Jesus Christ has always been led by living prophets and apostles. Though mortal and subject to human imperfection, the Lord’s servants are inspired to help us avoid obstacles that are spiritually life threatening and to help us pass safely through mortality to our final, ultimate, heavenly destination . . . While neither perfect nor infallible, these good men and women have been perfectly dedicated to leading the work of the Lord forward as He has directed.” (citation).

So we have multiple, recent witnesses that leaders aren’t perfect and that we aren’t supposed to expect perfection from them; D & C 1:19 actually warns against those who would “trust in the arm of flesh.” It’s long past time to stop wresting a few words from D & C 1:38 to imply that prophets are infallible.