(This needs some cleanup still)
Christ went to the spirit world between his death and his resurrection. There is a sort of Adam-ondi-Ahman type meeting going on there in the spirit world where Adam appears to have gathered his righteous descendants, waiting for Christ to appear, before Christ completes his conquest of death through resurrection.
Of Christ's visit to the spirit world we read
D&C 138:19 And there he preached to them the everlasting gospel, the doctrine of the resurrection and the redemption of mankind from the fall, and from individual sins on conditions of repentance.
There are a number of interesting things about this verse. The audience is the church as it exists in the spirit world. They know about the resurrection. But this is just before the beginning of the first resurrection where many of the dead who slept will be resurrected following Christ's own resurrection. (Brigham Young gives detail about the resurrection I'm not sure anybody else does, but I haven't studied it yet). So when Christ preaches the resurrection to them he is probably teaching them "how" it will take place rather than just teaching them "that" it will take place. Teaching about "the redemption of mankind from the fall" probably went into much greater depth that we currently understand given the timing and the audience. It is kind of fun to note that the audience even includes grandfather Adam who fell.
It is worth noting that Christ teaches them of "redemption" from "individual sins on conditions of repentance". That is the universal requirement for redemption from individual sins. This verse echos the article of faith "We believe that men will be punished for their own sins, and not for Adam's transgression" but it also adds an important detail. The condition on which men are redeemed from their individual sins is repentance.
That is an important clarification for us because there are those among us teaching the false ideas that at baptism we are made perfect, are clean every whit, and are sanctified by the blood of Christ. In short, these teachings assert that once we have a covenant we are saved in a sense close to that of modern protestantism.
But in the scriptures we find a different story than these protestant ideas. We read that we are redeemed from our individual sins on condition of repentance. That is a very different story, and a much more scriptural one. In that story, the cleansing effect of baptism does not extend (at least not in a lasting way) to any misbehavior we are continuing to do after baptism. We aren't sanctified, clean every whit, clean from the blood and sins of this generation, holy, perfect, sanctified and washed white in the blood of the lamb at baptism because baptism only offered us lasting cleanliness from the sins we were required to repent of in order to be baptized. Additionally, our goodness isn't added to Christ's goodness to add up to 100% goodness at baptism, nor does Christ's goodness supplant our own goodness thereby redefining all our future behavior to be acceptable before God because of our covenant with Christ.
As taught in the scripture we just read, the conditions of redemption for individual sins are not the mere existence of a covenant between us and Christ. The conditions of redemption for individual sins is repentance. Only then, after repentance, does Christ's atonement allow us to be forgiven and made clean of those sins.
In the scriptural story, baptism isn't a conclusion. Instead, baptism is a gate onto a path. At the gate we are given the gift of the Holy Ghost, are made clean of those things we repented of in order to be baptized, and our feet are set on a path.
But we are not clean every whit, we aren't clean from the blood and sins of this generation, we aren't kings and priests unto the most high God, and we aren't sanctified and washed white in the blood of the lamb just because we were baptized. Instead, the path our feet are put on at baptism is the path that will take us through all these things if we will press forward diligently along it, holding tightly to the iron rod. Our covenants mark the way for us to travel. We may not obtain all of these things in mortality, but we do the best we can so that we can have confidence that we will be allowed to continue the path in eternity to its conclusion.
And we see here in D&C 138 exactly that. We see Christ preaching to the righteous redemption from individual sins on conditions of repentance. This has application both to themselves, the righteous dead, as well as to those they will be carrying the gospel to. If we are not perfect when we die, which is what we expect, then we still have things to overcome, and so there is still a doctrine in the spirit world of redemption for individual sins on condition of repentance.
On a different note, it is worth noticing that does not mean God can tolerate sin in the least degree in his kingdom. The events in D&C 138 take place in the spirit world. They do not take place in the celestial kingdom of God. For Christ to visit this place appears to be unusual, and his followers are gathered and waiting for his appearance. What is more, the spirit world is here on this earth, whereas the scriptures inform us that the place where God lives is not a planet like this earth, but like a sea of glass and fire where he dwells in everlasting burnings. Thus there is perfect consistency in the scriptures. God cannot look upon sin with the least degree of allowance and no unclean thing can dwell in his presence. There are still individual sins in the spirit world because we are not perfect when we die, but there is also still repentance in the spirit world as well or it wouldn't make sense for Christ to be preaching it. The spirit world is not the place we obtain our eternal reward of dwelling forever with the Father and the Son, and so we don't have to be perfect by the time we get there. We still have time there to repent of our sins and continue along to the conclusion of the path we started at baptism.