1 Ne 21:9 That thou mayest say to the prisoners: Go forth

This refers to those spirits in spirit prison. Before Christ’s ministry in spirit paradise, there was a great gulf fixed which separated those in spirit paradise from those in spirit prison, see Lu 16:22-26. After Christ had established missionary forces among the righteous spirits, that gulf was bridged to some degree so that missionary work could begin among the spirits in prison. Those who accept the gospel of Jesus Christ will be released from prison. Whether this happens at their resurrection or at some earlier time is unclear. What is clear is that it was the Savior’s ministry in the world of spirits which makes it possible for them to go forth.

This passage is also included in Isaiah 61:1, 1-2, ‘THE Spirit of the Lord GOD is upon me; because the LORD hath anointed me to preach good tidings unto the meek; he hath sent me to bind up the brokenhearted, to proclaim liberty to the captives, and the opening of the prison to them that are bound; To proclaim the acceptable year of the LORD, and the day of vengeance of our God; to comfort all that mourn.’ This scripture was used by the Savior in a dramatic moment of his ministry. He read this passage in the synagogue and then said, This day is this scripture fulfilled in your ears. He was telling the people of Nazareth that he was the Messiah, the one to whom Isaiah was referring. This prompted the response, Is not this Joseph’s son? (Lu 4:16-24)

Jeffrey R. Holland

“Christ brought freedom to mortal beings imprisoned by ignorance, sin, apostasy, and death. He also brought deliverance to those on the other side of the veil who had not heard the gospel but would receive it in their spirit prison. Peter taught this clearly, and the whole of section 138 of the Doctrine and Covenants is devoted to this glorious doctrine…On both sides of the veil, the captives rejoice and praise their God as Christ throws wide the prison doors.” (Christ and the New Covenant: The Messianic Message of the Book of Mormon [Salt Lake City: Deseret Book Co., 1997], 83.)