From Revelations of the Restoration, 1140:
The question could well be asked as to why it was that Alvin would be chosen to represent these truths [redemption of the dead]? The answer is that he is the perfect example of hte kind of person to whom these principles apply. Alvin died in November of 1823. His passing had been a matter of considerable sorrow to the Smith family and to the young woman to whom he was engaged. Their wounded souls had been cut to the core at his funeral by an the unfeeling remarks of the Presbyterian minister who had consigned Alvin to hell because he had not been baptized or involved in that church.
Despite his relative youth, Alvin was a man of unusual spiritual propensity. Before his death, he called each of his brothers and sisters in turn to his bedside and gave them a parting admonition. To his eighteen-year-old brother, Joseph, he said: "Be a good boy, and do everything that lies in your power to obtain the record [the Book of Mormon]. Be faithful in receiving instruction and in keeping every commandment that is given you" (Smith, History o f Joseph Smith, 1996, 116). Mother Smith stated that "Alvin had ever manifested a greater zeal and anxiety, if ti were possible, than any of the rest with regard to the record which had been shown to Joseph, and he always showed the most intense interest concerning the matter. With this before our minds, we could not endure to hear or say one word upon that subject, for the moment that Joseph spoke of the record it would immediately bring Alvin to our minds with all his kindness, his affection, his zeal, and piety. And when we looked to his place and realized that he was gone from it, to return no more in this life, we all wept with one accord over our irretrievable loss, and we 'could not be comforted, because he was not'" (Smith, History of Joseph Smith, 1996, 119).
Nearly twenty years later, Joseph Smith recounted his feelings at the time of Alvin's death, saying: "I remember well the pangs of sorrow that swelled my youthful bosom and almost burst my tender heart when he died. He was the oldest and noblest of my father's family. . . . He lived without spot form the time he was a child. . . . He was one of the soberest of men, and when he died the angel of the Lord visited him in his last moments" (History of the Church, 5:126-127).
I love this quote; I always thought that the vision of Alvin with his parents must have been so poignant for Joseph because they had been so close.