In the previous chapter, the Lord recognized the great faith of the brother of Jared by allowing him to view the body that He would inhabit as Christ on the earth. The Lord also showed him things that would happen through the end of the world. Ether 3 ends with the Lord commanding the brother of Jared to write down what he saw, such that this record could be shared with future generations.
In Ether 4, the Lord instructs Moroni in how to handle the record of the brother of Jared. He is told to "seal up" the writings such that "they shall not go forth unto the Gentiles until the day that they shall repent of their iniquity, and become clean before the Lord" (verse 6).
On the one hand, the call to repentance is typically directed at those who have not yet given their lives to the Lord, even as it is at the end of this chapter — "repent all ye ends of the earth, and come unto me, and believe in my gospel, and be baptized in my name" (verse 18).
On the other hand, even servants of God can be prone to sinful actions or attitudes that require repentance. Lest we're quick to say, "Not me — I'm not doing anything wrong," remember that pride, envy, lack of forgiveness, and lack of love toward others all qualify as behaviors that should not exist in a servant of God.