The people are under condemnation for rejecting belief in the coming Messiah. They have exchanged the God of their fathers for greed and materialism.
Reference: Nephi’s words obviously echo Matthew 6:19–20 (compare the similar reference in Helaman 5:8):
Lay not up for yourselves treasures upon earth, where moth and rust doth corrupt, and where thieves break through and steal:
But lay up for yourselves treasures in heaven, where neither moth nor rust doth corrupt, and where thieves do not break through nor steal.
Nephi certainly wanted to contrast heaven’s eternal treasures with the world’s temporary ones. However, Joseph clothed that concept in language drawn from King James Version. As the differences show, however, Joseph was not merely copying but rather was influenced by his memory of the passage in capturing the idea on the plates.