D&C 20

 We are taught the Lord gave the Prophet Joseph Smith - 

"...power from on high, by the means which were before prepared, to translate the Book of Mormon;

9 Which contains a record of a fallen people, and the fulness of the gospel of Jesus Christ to the Gentiles and to the Jews also;

10 Which was given by inspiration, and is confirmed to others by the ministering of angels, and is declared unto the world by them—"  (Doctrine and Covenants 20:8–10)

It becomes clear that ministering angels are aggressively confirming the truth of The Book of Mormon to the world.

Also that The Book of Mormon contains - 

"...the fulness of the gospel of Jesus Christ..."  (Doctrine and Covenants 20:9)

In my mind, the law of the "gospel of Jesus Christ" is taught in the temple.  Sherem also suggested - 

"...gospel, or the doctrine of Christ."  (Jacob 7:6)

were being taught as one of the same.