Doctrine and Covenants 42: 11-14 are in many ways a repetition of D&C 20. In fact the question asked by the gathered elders was how to act upon the law while they were waiting for Zion.
Verse 11 dictates that any person who preaches or builds up the church must follow this procedure: they must be one, ordained, two, ordained by someone with authority, and three, the people of the church know that the person ordaining has authority. D&C 20: 60-67 lay out the rules of ordaining elders, priests, teachers, and deacons. Verse 60 states that all of these must be ordained, ordained by one with “power of the Holy Ghost,” and verse 64 says that these “may take a certificate from him at the time, which certificate, when presented to an elder, shall entitle him to a license, which shall authorize him to perform the duties of his calling.” Additional details are given in verses 62-62 and 65-67. The short account in D&C 42 verse 11 is simply a summary of the instruction already given in D&C 20:60-67.
D&C 42 verse 12 explains what the elders, priests, and teachers ought to teach. They are instructed to “teach the principles of the gospel, which are in the Bible and the Book of Mormon.” Verse 12 also notes that the Book of Mormon has a “fulness of the gospel.” D&C 20 does not include specific instructions on what to teach, but verses 17-36 are dedicated to rehearsing some of these “principles of the gospel.” President Benson saw these verses as “summarizing the vital truths which the Book of Mormon teaches.” Verse 9, like D&C 42:12, also states that the Book of Mormon “contains … the fulness of the gospel of Jesus Christ.” Verses 11-12 of D&C 20 suggest that the Book of Mormon “proves to the world” that the Bible and its principles are true.
Verse 13 of D&C 42 refers the elders, priests and teachers directly to D&C 20, calling the text the “covenants and church articles.” They are also told to teach “as they shall be directed by the Spirit.” D&C 20:45 gives this direction to the elders (and by implication of verse 49 and 56, to the priests and teachers as well): “The elders are to conduct the meetings as they are led by the Holy Ghost, according to the commandments and revelations of God.” D&C 42:13 has a similar formula: rely on the things already written as led by the Spirit.
Verse 14 is where this short passage goes beyond summarizing D&C 20. Verse 14 reads: “And the Spirit shall be given unto you by the prayer of faith; and if ye receive not the Spirit ye shall not teach.”
This verse points beyond D&C 20 and D&C 42 to the following sections, primarily D&C 46 and 50.