I agree with: "the words "dead", "alive again" "lost," and "found" are spiritual terms" in the context they are used, however I do not think the intended main point of the parable is what you seem to suggest. The main point, as redleghunter pointed out, is the graciousness unmerited favor of the father. The intention is not to teach fine points of theology, or to create a puzzle, usually they are intended to teach one main point, in the form of stories, perhaps to make them memorable to the hearers. The problem comes in the tendency to treat the spiritual lines of a parable as allegory (repentance is more spiritual than physical, but tends to be both), and it has a detracting if not disassembling effect on the main point.
First, the Bible is consistent in it's use of spiritual terms. Dead means dead in reference to talking spiritually. Lost means lost when talking spiritually. Unless you can prove otherwise with the Bible. For what does the word "dead," "lost," "found," "alive again" mean to you in the Parable of the Prodigal Son? They are speaking in spiritual terms because the son was not physically dead and or physically lost.
Second, the Parable of the Prodigal Son is about repentance for two reasons. One, in the Parable of the Prodigal Son, the son plans to repent towards his father to remedy his situation in being reconciled with his father. When he returns home he does exactly that. For the son repents and his father accepts it and there is great rejoicing. Two, the other previous parables are also talking about repentance. So there is a continued theme or point going on here. In the Parable of the Lost Sheep, Jesus says that he goes out and looks for a single lost sheep. When he finds this one lost sheep, he says he rejoices greatly. This is compared to how when a sinner repents, there is great rejoicing in Heaven (Please read Luke 15:1-7 again; And then re-read verse 7 very slowly going over each word with a fine-toothed comb). In the Parable of the Lost Coin, a woman loses her coin (treasure) and she then searches for it diligently and finds it again. The coin or treasure is Jesus Christ. 2 Corinthians 4:7 says we have this treasure (Jesus) in earthen vessels (our bodies) showing us that excellency of all true power is of God and not of us. Anyways, when she loses the coin (i.e. the treasure who is Jesus), and she then finds it again, she rejoices greatly. This is then compared to the great rejoicing that happens when one sinner that repents. The Parable of the Prodigal Son is no different. The Prodigal Son comes home with him repenting of him going prodigal (i.e of him being in sin away from the father), and he is then restored and there is great rejoicing. Not sure how you cannot see this obvious lesson in Luke 15. It is very clear, to those who want to see it.
But what does repentance mean? The Parable of the Prodigal Son in light of the previous two parables defines it's meaning for us. Repentance is seeking forgiveness of one's sins with the Lord. This is exactly what the Prodigal Son did whereby there was great rejoicing (Which is what we see in ALL three parables).
In fact, Jesus defines this meaning of repentance again elsewhere for us in Scripture. In Matthew 12:41, Jesus says that the Ninevites will rise up in judgment against this generation because they repented at the preaching of Jonah. If you were to turn to Jonah 3:6-10, you would be able to read that the King of the Ninevites had told his people to do two very important things.
#1. Cry unto God (i.e. Seek God's forgiveness, Repentance).
#2. Forsake your wicked ways (i.e. the Natural Fruits of Repentance).
Note: Remember, in the NT: John the Baptist told men to bring forth fruits (deeds or actions) worthy of repentance. Meaning to bring forth a changed new life that obeys God's moral laws and who remains fruitful.
Anyways, when God had seen the Ninevites forsake their evil ways, that was the time that God decided to turn back from his bringing wrath or judgment upon the city of Nineveh. So we see that true repentance is seeking God's forgiveness (that is followed by the fruits of repentance, i.e. forsaking one's evil ways). For one is not really sorry about their sin if they turn back around and start to do evil again.
For the son that did the will of the father was the son who repented and actually did what his father said (See the Parable of the Two Sons in Matthew 21:28-32).
I mean, how do you get past things like these?
They are very clear to me when I read it.
How about things like Matthew 25:31-46?
It is essentially saying that if we do not help the poor in this life, we will be cast into everlasting fire.
What about the Parable of the Talents in Matthew 25:14-30?
The one who was faithful over a few things was told this by the Lord,
"Well done, thou good and faithful servant: thou hast been faithful over a few things, ... enter thou into the joy of thy lord." (See Matthew 25:21). In other words, the Lord did NOT say, "Good job for trusting in my death and resurrection alone while you ignored doing good works and in obeying me .... please enter thou into the joy of thy Lord." In fact, the unprofitable servant is cast into outer darkness where there is weeping and gnashing of teeth (Matthew 25:30). Gnashing of teeth is also what wolves do. Check out the spoiler image below to see what I am talking about.
Oh, and here is a human example:
