I'll reference the old Bible story how Jesus went and preached to the spirits that are dead (see 1 Peter 3-4). I will also reference the old Bible and how it brings up baptism for the dead as Paul argues for the resurrection (see 1 Corinthians 15). I would argue that paradise is not salvation into the kingdom of heaven but a place among the spirits who are dead who receive the teachings of Jesus. Jesus told the man on the cross that he would be with him that very day in paradise. Upon Jesus' death and before his resurrection he went among the spirit of the dead preached his gospel. It was not until the 3rd day that Jesus was resurrected and it was then that he told Mary to not touch him because he had not yet ascended to his Father in heaven. Thus the man on the cross could not have been in heaven with Christ on that very day since Christ had not ascended until after the 3rd day. He was with Jesus among the spirits of the dead. Those among the dead who accept the gospel are in spirit paradise while those who have not accepted the gospel among the spirits who are dead are in spirit prison.
In the true church of Jesus Christ, the doctrine of baptism for the dead is a true principle and the living can perform vicarious baptisms for the dead. Thus all can receive baptism even if they are dead. So yes, baptism is required to enter the kingdom of heaven but is still available by proxy even for those who are dead. During the Millennium, this will be one of the great works performed on this earth to bring all the opportunity to enter the kingdom of heaven.
