1 Nephi 15:14
14 And at that day shall the remnant of our seed know that they are of the house of Israel, and that they are the covenant people of the Lord; and then shall they know and come to the knowledge of their forefathers, and also to the knowledge of the gospel of their Redeemer, which was ministered unto their fathers by him; wherefore, they shall come to the knowledge of their Redeemer and the very points of his doctrine, that they may know how to come unto him and be saved.
Nephi had just told his brothers that if they hardened their hearts—chose not to know the mysteries of godliness—they would perish, but, “If ye will not harden your hearts…surely these things shall be made known unto you.” After Nephi explained that his father had likened the house of Israel, including their own descendants, to an olive tree, he also told them why it was so important that they know. The sequence of thought he follows is important.
Even though one is not held responsible for sins he does not know are sins, it is also true that no unclean thing can be where God is. Consequently, one cannot be saved unless he knows how to come to the Savior and be saved by him. If we do not have the opportunity to learn while we are in this life, we will have it in the next. But the fact remains that we must know, and we must let that knowledge be the pilot of our actions. Therefore, it was very important to Nephi to know that ultimately their descendants would “come to the knowledge of their Redeemer and the very points of his doctrine, that they may know how to come unto him and be saved”(1 Nephi 15:14). Having explained that one must “know how to come unto him and be saved,” Nephi then promises his brothers that their descendants would come to that knowledge in the last days.