Verses 4 and 5 are clearly the ones that members of the Church of Jesus Christ of Latter-day Saints have heard most often, but they are part of this longer thought. The connection, in the beginning, is the “I would exhort you,” which we see in both verses 3 and 4. While we are exhorted to ask “if these things are not true,” we are also asked to remember “how merciful the Lord hath been unto the children of men, from the creation of Adam even down until the time that ye shall receive these things.”
Verse 3 sets the context for the asking in verse 4. The Lord has done prodigious works among his children, and Moroni exhorts us to see the Book of Mormon in that light, as yet another demonstration of the love of God for his children on earth.
Verse 5 invokes the Holy Ghost to know truth, and verse 6 reminds us that “nothing that is good denieth the Christ.” Moroni intentionally references his father’s sermon which Moroni included in Moroni 7 (verses 19–25). Finally, verse 7 declares that understanding the message of the Book of Mormon is equivalent to understanding that Jesus is the Christ.
Some have questioned the phrase “if these things are not true” as an awkward way to ask for truth. This is simply a different way of saying the same thing as “Ask if these things are true.” However, the “not” seems to act as an intensifier, suggesting, of course, that they are true. It is like asking: “Is it not so?” That short interrogatory sentence is another example of this use of “not”; it really doesn’t mean a negation.