1 Nephi 10:4-6

The whole point of the Book of Mormon is to testify of Christ. Christ is the center of the whole Plan of Salvation, which means that every prophet from the beginning of time down to this point of Nephi's life has testified that a Savior will come to save all men. Verse 4 states exactly when it will happen and that Christ will be a Savior. Verse 5 states again that Lehi knows that Christ is the Redeemer and that is was the subject of all the prophets sayings. Verse 6, we are lost and fallen, and will ever be so, unless we rely on our Savior.

Lehi is exhorting Laman and Lemuel to do these things. They will be lost and fallen forever, if they don't believe in Christ and work hard to follow His commandments until the end. This is the true doctrine, perhaps the most important one because it's the one that Lehi tries so hard to teach them. I know that understanding our role with respect to the Savior's in the great Plan of Salvation is the most important thing, and how great the need have we to help other's understand that as well.