Anciently, why would a scribe have a seal? When a scribe wrote an official document (such as a legal contract, a divorce decree, or a promissory note), the scribe would bind the written record, tie it up, put a lump of clay or wax on the knot, and imprint his seal in the clay or wax to indicate that the record was an official, formal, correct document. This is how official transactions were conducted in ancient times. Notice that in 2 Nephi 27, Nephi knows that there will be a record. It will be witnessed by three witnesses, and it will be sealed, meaning that the record will not just be closed up, but that it will be preserved with seals of authority. Sealing important documents that directly affected the life of an individual was part of Nephi’s world. We can learn something from the fact that the record of the Nephites was witnessed and sealed. It is important to ascertain the attestation and testimony of those who influence us in making decisions that affect our eternal life.
Book of Mormon Central, "Why Would a Book Be Sealed? (2 Nephi 27:10)," KnoWhy 53 (March 14, 2016).