Complex sentence: Yet almost immediately upon their exile, Lehi is commanded by God to send his sons back to Jerusalem to retrieve the brass plates, a record similar to the Old Testament which was owned by Laban, a powerful leader in Jerusalem.
Split into simpler sentences: Yet almost immediately upon their exile, Lehi is commanded by God to send his sons back to Jerusalem to retrieve the brass plates. The brass plates are a record similar to what the Old Testament is, owned by Laban, a powerful leader in Jerusalem.