The command to search these things is repeated for the third time on this same day. Once again it comes in connection with Isaiah, although there is no reason to suppose that Isaiah is the only prophet profitable to search.
There is little transition given as Mormon moves to the insertion of text from Malachi. The Savior cited Isaiah, now the Savior cites Malachi. The context has been one of discussing the value of the written text. Malachi’s text discusses the events of the end of time, which was the subject of the previous discourse by the Messiah. The themes become tied together in an important way in this chapter of Malachi in verse 16 below.
[I will send my messenger, and he shall prepare the way before me]: An event is about to take place, but it will not happen without being announced. There are several contexts in which this messenger may be seen. One is that it is John the Baptist as the messenger before the mortal mission of the Savior. While that might be possible, the context of this chapter in Malachi deals with the last days, not the mortal ministry of the Savior.
It would appear to be best to read the messenger as a prophet who prepares the world for the second coming. In this case, it is not unseemly to suppose that Joseph Smith is a reference here, particularly as the Savior is citing texts that may have a unique perspective for his New World audience. He has already laid the groundwork for the coming forth of the Book of Mormon as a major event signaling the beginning of the end of times, and Joseph Smith obviously fits into that context as a messenger sent to prepare the way and introduce the Book of Mormon.
[the Lord whom ye seek shall suddenly come to his temple]: The second coming of the Messiah will be sudden. This verse must have thundered in the consciousness of those in Bountiful, who had just the day before seen their Messiah suddenly come to his temple! More than any other people known to us, these saints in Bountiful knew that the Messiah could certainly come suddenly to his temple. He did so, and was there with them. For them it would be very easy to believe that when the mission of the Atoning Messiah was ended, the mission of the Triumphant Messiah might have a similar beginning.
In the context of the sermon earlier in this same day, the saints in Bountiful would hear the temple as the temple in the New Jerusalem.
Textual: To better replicate the way that Mormon constructed this particular chapter, the last verse of the previous chapter is repeated here where it was originally placed in the 1830 edition.
Malachi was a prophet who wrote after the Lehites had left Jerusalem. The Savior understood this, and it is explained to the assembly in 3 Nephi 26:2.