"And again, blessed are all they that mourn, for they shall be comforted."
This is unconditional. "All" are included. "All they that mourn" will be blessed.
Between sessions of conference Saturday I attended a friend's funeral. Mourning because of death is the first cause we associate with this promise. Over death, however, He has gained the victory. It was His mission and ministry to bring about victory over death. "And he will take upon him death, that he may loose the bands of death." (Alma 7: 12.) This done now, though death continues to claim all of us. We know we will have part in His victory. Comfort from that victory will come to us all.
Death is not the only cause of mourning, however. We all experience afflictions, troubles, temptations, and pains while mortal. He has gained the victory over all of these also: "And he shall go forth, suffering pains and afflictions and temptations of every kind; and this that the word might be fulfilled which saith he will take upon him the pains and the sicknesses of his people. And he will take upon him death, that he may loose the bands of death which bind his people; and he will take upon him their infirmities, that his bowels may be filled with mercy, according to the flesh, that he may know according to the flesh how to succor his people according to their infirmities. Now the Spirit knoweth all things; nevertheless the Son of God suffereth according to the flesh that he might take upon him the sins of his people, that he might blot out their transgressions according to the power of his deliverance; and now behold, this is the testimony which is in me." (Alma 7: 11-13.)
Do you mourn because of afflictions? Temptations? Pains? Sickness? Infirmities? The troubles of the flesh? Sins and transgressions? It does not matter the cause of your mourning, Christ has suffered all these things so that He may understand the troubles of the flesh and, by understanding them to overcome them all. By overcoming them all, He then in turn can share the victory.
Your failures are not going to be reason to punish you. If you repent, they will be lessons from which to learn. The guilt will be removed, you will be comforted, and the lessons will remain. Your mortal trials will confer upon you the taste of the fruit of the tree of knowledge of good and evil. (Gen. 3: 17-19.) You will have learned from what you suffer the difference between the two, and have the benefit of Christ's atonement to remove all guilt. (2 Nephi 2: 26.)
All will be comforted from every offense they have ever suffered. All that remains will be the choices you have made. (Moroni 7: 16-17.) The offenses you suffered at the hands of others will be made up to you. All infirmities you have been plagued with while mortal will be removed. (Alma 40: 23.) Only your choices will remain as either a continuing blessing or continuing affliction. But that is your choice. (Alma 41: 13-14; Moroni 7: 18-19.)
Earth's valuable lessons will remain with you, and inform you eternally with knowledge of good and evil. In this you will have become like God. (Gen. 3: 22.) But the experiences you suffer, which are the means of learning good from evil, will all be removed. You will no longer "mourn" for anything. You will, however, remain accountable for your choices.
This is the perfectly balanced experience. Through it we learn and gain experience (Abr. 3: 25-26), but we are only burdened by what we voluntarily impose upon ourselves through our choices. (1 Nephi 15: 32-33.) The promised "comfort" against our mourning will be complete if we have chosen to follow Christ, and incomplete if we have chosen to reject Him. Because He can only remove all the burdens of nature and mortality imposed as a condition of life here, He cannot remove those voluntarily assumed by wrong choice while living here. (Mosiah 16: 8-13.)
The balance between necessary experience and accountability is maintained. Through Christ are all things made possible.