If someone has committed a serious sin that resulted in excommunication – and has since gone though full repentance process, was re-baptized and all their blessings were restored – why do they still have to endure the consequences of their actions many years (decades) later. Why does the Lord not heal/take away those consequences with full forgiveness?
Without knowing more details, it is hard to say specifically, but I can give you a general answer.
Unfortunately, the nature of this life is that some consequences of our actions don’t go away even with full forgiveness. You may have heard the analogy of putting nails in a fence (the sin) and then removing them (repentance). Even though the nails have been removed, there will still be holes in the fence. Or to give a more concrete example,
Consider a young couple who makes a mistake and violates the law of chastity. Imagine that the young woman gets pregnant. Even if the young couple repents and is forgiven, there is still going to be a baby. That baby is both a consequence of this couple’s actions, and a blessing to the family who raises him/her (whether the baby is kept by the couple or given up for adoption, it will be a blessing to someone.)
What if a teenager gets drunk and drives? Suppose while that teen is driving he gets in an accident and someone else is killed? Even though the teen might repent and be completely forgiven, by both God and the people he harmed, the person who died will not be coming back.
Say for example, a married woman has an affair. As a result, she is divorced and excommunicated, but she repents, is rebaptized and has all of her blessings restored. Perhaps she even remarries to a good man in the temple, and they are happy. That doesn’t take away the pain her choices caused her children, or those who love her.
While it may seem unfair that someone continues to suffer the consequences of a sin long after they have repented and been forgiven, consider also the unfairness of those innocent people who suffer because of other people’s sins. A child who is molested will have to deal with the consequences of that sin for many years to come, though he or she did nothing wrong. All this unfairness is one of the reasons we need the Atonement.
The Savior suffered more than any of us can understand, and he was innocent too. He suffered the pain of the sinners (which is all of us) and of those who are sinned against. Because of his atonement we not only have the ability to repent and be forgiven, but He can succor us in our pain . . . whether that pain comes from our own choices or those or others, and the pain of consequences of sins repented of and forgiven.
There is truly much in this life that is not fair, but Christ is our hope. Through Him, some day all things will be made right, and all suffering will be consecrated to our good.