Elder Bruce R. McConkie has written:
“Before Christ bridged the gulf between paradise and hell- so that the righteous could mingle with the wicked and preach them the gospel- the wicked in hell were confined to locations which precluded them from contact with the righteous in paradise… .
Now that the righteous spirits in paradise have been commissioned to carry the message of salvation to the wicked spirits in hell, there is a certain amount of mingling together of the good and bad spirits. Repentance opens the prison doors to the spirits in hell; it enables those bound with the chains of hell to free themselves from darkness, unbelief, ignorance, and sin.
As rapidly as they can overcome these obstacles- gain light, believe truth, acquire intelligence, cast off sin, and break the chains of hell- they can leave the hell that imprisons them and dwell with the righteous in the peace of paradise.” (Mormon Doctrine, p. 755.)