Nephi now returns to emphasize the problem of "what to do." He indicates that he has given them the sum total of the doctrine of Christ that they will receive until such time as the Messiah comes in the flesh. The implication is that the arrival of the Messiah will alter practice, but that current practice (Law of Moses) will continue until that time. Only after that arrival of the Messiah in the flesh will new instructions be given that people entering into the covenant "shall…observe to do" (emphasis added.)
What then is this doctrine of Christ? For Nephi it consists of the covenant, witnessed by baptism, the gift of the Holy Ghost, and personal revelation through the Holy Ghost that will individually teach the person what they need to do to follow through on their covenant. One may presume that the kind of things that are expected follow the same examples Christ will give during the Sermon on the Mount, where he will emphasize the internalization of the reasons for the actions of the Law.