Kolo, there are a couple of things you say here that I think are eisegetical.
First of hall, the idea that the son 'had to' go through all of these things to come back. I don't believe that is the case. The son, as a son, could have turned around at any point and could have avoided a whole lot of bad effects of the sin in his life. Nothing made him cease being a son. He didn't realize this for he would have disowned himself if the shoe were on the other foot - yet, he was born a son and nothing could make him cease from being a son. Not even 'death'.
Second, I think it is eisegesis that the son realized how much he loved the father. I don't know that we see that here. He realized what he had done wasn't working. He remembered the good old days with the father. But he hoped that he could make a deal with the father to where he could be a servant. He just knew he couldn't be a son any more - after all, that's the way he himself would have treated any son who had done to him what he had done to the father- if even that good. So, devoid of anything he could offer the father but service, he went with his tail between his legs to beg for mercy. I think the love for the Father came after he experienced the Father's mercy (and is something we don't see in the parable)- for only after his restoration could he understand and appreciate how great the Father's love was for him.
It is true, the greeting of the Father is of key importance to the parable. The Father saw the son and went running to him. The son had nothing, could do nothing, came empty handed. The Father, out of pure grace, mercy, and love, restored him to all of his former glory.
But there is another point that all of us have ignorred here. It is in the elder son.
The elder son did all the right things, stayed with the Father, and he never strayed. He was the poster-boy for right living. When the son who had strayed returned, the elder son was indignant. He said "look at me! I stayed with you. I served you faithfully these many years. I never transgressed! Look at how good I was. And this other son, he spent all of your blessings on depravity! And yet, you accept him back and give him your very best! " (definite paraphrase)
At this point, in the parable, Jesus does something interesting. In verse 31, rather than calling him "huios" or "son" (a term used throughout the parable to this point), he says "teknon" or "child".
Since Jesus is speaking to the Pharisees, his overall point seems to be that the faithful children of the Father should rejoice and not act like spoiled children when the one who has strayed returns and love that person as a full brother without undue burden or conditions of acceptance.
"First of hall, the idea that the son 'had to' go through all of these things to come back. I don't believe that is the case."
In this parable, the fact is that he did go through all those things...and that's what lead him to die to his own selfishness and become humble before his father. It doesn't have to happen the way it happened to the son in the parable, but all of us, in one way or the other, have to die to the self and become humble before God.
"I think it is eisegesis that the son realized how much he loved the father. I don't know that we see that here. He realized what he had done wasn't working. He remembered the good old days with the father. But he hoped that he could make a deal with the father to where he could be a servant. He just knew he couldn't be a son any more - after all, that's the way he himself would have treated any son who had done to him what he had done to the father- if even that good. So, devoid of anything he could offer the father but service, he went with his tail between his legs to beg for mercy."
The Fathers say that this is a demonstration that he did still love his father, because he was humiliated and returned with his tail between his legs ready to be a slave, but he did that because he remembered that he loved his father. If he scorned his father, the Fathers teach, he would not have returned. The truth is, many, maybe even most, people don't return.
"But there is another point that all of us have ignorred here. It is in the elder son."
Very good! The Fathers wrote at length about the elder brother and to tell the truth, I have heard more sermons from orthodox priests about him than the younger brother!
In Orthodoxy, we call this parable "The Parable of The Two Sons". And you are very right about the Pharisees. What the older brother represents is a lack of love and mercy and compassion, but mostly a lack of love. He "did" everything right, played by all the rules, but condemned himself by his jealousy as one who had learned nothing except arrogance and a sense of entitlement which lead not to experiencing the love his father showed, not to becoming like his father, but rather the opposite, consumed with hatred.