This general principle is addressed first. Nephi will build on it in the following verses. But the first statement is the broadest.
An earlier "wo" was pronounced upon those who rely on the uninspired teachings of men who use their own precepts. Now he adds a second "wo" to those who also deny the need for continuing revelation. We claim we are unlike all other faiths because we believe in the concept of continuing revelation. However, that notion is greatly modified by us to the point where the continuation of revelation is so limited, so curtailed, and so distrusted that we are generally unacquainted with any new revelation.
Do we hear of visions and visitations? Not much, if at all. We think that such things are reserved for leaders. For example, if Elijah were to return with a message to someone, we would expect the person with whom he would visit would be the church President. If it were someone other than the church President, we would instantly be suspicious because Elijah wasn't following the "chain of authority" as we expect. [Interestingly, as soon as you know Elijah was involved you should consider that another line of authority may be created.] So even if we heard from Elijah, it would cause us trouble and likely be rejected as too irregular. This would be true of other heavenly messengers, as well.
What visitations could we tolerate? Pretty much we'd only think it appropriate for an ancestor to visit with a descendant to give a family message. A deceased great-grandfather coming to bring a message about one of his descendants would seem to fit within the whole "chain of authority" model we have created. Family business. Seems to be acceptable. However, even then, we would expect the person involved to "keep it to themselves" because it was inappropriate to share things like that. Too personal. Too sacred. Too much information of a deeply personal nature to warrant talking about it with others.
What if the great-grandfather were Abraham? Would that fit the model? What if his concerns ran to all who are living? Would that family be large enough to warrant talking about it with almost anyone? Oops, we're back to the whole "chain of authority" argument again, and would expect Abraham to limit his visit to the chief Mormon-in-charge. So a visit by Abraham would be suspect as well.
What if the message were from John the Beloved? He has a continuing ministry to visit with people and bring them to salvation. In fact, his ministry includes visiting with those who will be "heirs of salvation who dwell on the earth." (D&C 7: 1-6.) Still, if a person had him minister to him, we would not want to hear about it, would question the propriety, and wonder why John would come when other perfectly authoritative men are living on the earth inside the church holding the same keys as John. So, that would be questioned and regarded as irregular as well.
So as Latter-day Saints we believe in the continuation of revelation, visitations, visions, etc. so long as they conform to our limited model, come to the right person, and don't disturb anything we have going on at the present. Which is to say we don't believe in continuing revelation much at all.
What about Christ? Can He visit with anyone whom He deigns to visit? That's a little closer call, because He seems to have promised to come to all. He also displayed remarkably democratic tendencies both on the day of His resurrection, and when visiting the Nephites. (I've explained His disregard for the church hierarchy He established on the day of His resurrection in Come, Let Us Adore Him.) He seems much less interested in respecting established religious authority than we do. So we might allow the Lord to visit with someone, but, then we wouldn't want to hear many details because that would be wrong for some reason. Probably "casting pearls before swine" or "profaning" or "disrespecting the line of authority" or something. Not sure which one, but there's got to be a prohibition against it somewhere.
So we have tendencies that are difficult to put into a hard and fast rule, but I'm going to attempt it
Rule 1: We believe in continuing revelation; predicated upon the following:
Well, We believe all that God has revealed to authorized people in positions of authority, all that He does now reveal, and we believe that He will yet reveal to the proper channels many great and important things pertaining to the Kingdom of God; and that once it has been reviewed by the Correlation Department and published by Deseret Book it will become something which we can all accept as being from an authorized source and reliable.
Until that happens, we have absolutely received enough of the word of God and we don't need any more of the word of God. And, by damn, if someone comes claiming revelation or an independent apostolic witness of the Lord's resurrection we will want them to cut off an arm or some other member of the body and then restore it again, so that we may know he has come with power. I'm quite confident that ought to satisfy our need to see a sign before we will believe a proposition.
Now we know for certain Nephi's warning is to those other faiths that do not accept continuing revelation and not to us. However, as to those, Nephi has pronounced a prior "wo" for their acceptance of the precepts of men, and now a second "wo" upon them for their refusal to accept continuing revelation. These begin to mount up and ought to worry those to whom these concerns are addressed, whoever they may be. Perhaps Nephi should have written his book for those people, instead of us good folks who read the book and know for certain that we're alright.