A friend and I recently had a conversation about applications of the parable of the Prodigal Son in our lives (see her post) and it got me thinking on several points on the interpretation of this parable.
When asked about the interpretation of this parable, Joseph Smith taught "I have a key by which I understand the scriptures. I enquire, what was the question which drew out the answer, or caused Jesus to utter the parable?" (Teachings of the Prophet Joseph Smith, pg 277). The Pharisees were criticizing Christ for sitting with sinners. He then taught several parables regarding the rejoicing over those who repent.
The parable of the Prodigal Son stands out to us among those because we get a more intimate look into their lives.
One lesson we gain by this more intimate look is that there is not just rejoicing over a lost child of God but that in their journey back they can and should aim high. The prodigal son came back only aiming for telestial, maybe terrestrial, glory in asking to be a servant (see D&C 76:112). The father told his son to set his sights higher, to that of the celestial kingdom, by acknowledging their kinship (see D&C 76:56-58).
Another lesson is from the Other Son. We get the reminder to not be jealous of the rejoicing for the returned sinner (see Elder Holland, The Other Prodigal. There is sadly a tendency though to over-analyze this son since those who would do such analysis probably see more of themself in this son than the prodigal son. Within the overall context of the parable, one might try to make the Other Son a surrogate for the Pharisees. President Kimball warned against being overly harsh in judging the Other Son and taught that it is better to have not sinned than to have sinned and repented (Spencer W Kimball, Miracle of Forgiveness, Chapter 20).
Focusing too much on the Other Son loses our focus on what the focus of this parable is (rejoicing when sinners repent and come back). We end up incessantly playing a single note tune similar to the pitfall of gospel hobbies which Elder Packer warned about:
Some members of the Church who should know better pick out a hobby key or two and tap them incessantly, to the irritation of those around them. They can dull their own spiritual sensitivities. They lose track that there is a fulness of the gospel, . . . [which they reject] in preference to a favorite note. This becomes exaggerated and distorted, leading them away into apostasy.
Reading the Other Son's words in context of the teaching setting, he seems to be there to fulfill the role of an "audience surrogate" (WARNING: TV Tropes) so we gain an understanding of the father's thoughts. This doesn't diminish the opportunity to learn from the Other Son but it puts it in context to not look beyond the mark.
Analogies break down after a certain point and looking past that can lead to a skewed perspective on the gospel. We don't see is what happens to the Prodigal Son in the long run. The truth being taught has been covered. We can extrapolate a couple of possibilities based on gospel truths we already know.
The first is the more sad to contemplate intepretation. The Prodigal Son returned to the presence of his father but with his inheritance wasted much as David had fallen from his exaltation (see D&C 132:39). I think its much better to contemplate on the interpretation that I would hope would be more broadly applicable and with much less dire results. This interpretation ends right where Christ does. Unlike an inheritance from an earthly father, the inheritance from our Heavenly Father is not zero-sum, to give to one son does not diminish from another. There is infinitely more to dole out to those who squandered but repent. There is hope for something unfathomably great for those who repent.