Answer:
a) The main theme that Jesus is communicating is the importance of seeking forgiveness no matter how heavy or serious the offense may be.
b) The three characters are the father, the elder and and the younger son/the prodigal son.
Explanation:
a) In the parable of "The Prodigal Son", the main theme that Jesus emphasizes and wants to show is not the return of the son nor the celebration of his return. But rather, the focus should be on the importance of asking for forgiveness. The bravery or the courage to seek forgiveness even after committing a serious mistake is the moral of the story.
b) The three main primary characters of the story are the father, and the two sons.
The father epitomizes our loving Father,God who is ever ready to welcome us with open arms irrespective of all the mistakes me make. God is always eager for us to return to him no matter what sins we may have committed. As long as we have the courage to ask for forgiveness, he is always ready to welcome us to his home.
The elder son is an example of a Christian who may be good but still fail to act like a Christian should. His relationship with God may be good and he may do everything that he is told, leading a good Christian life but this dormant life is not what matters. He still has complains whenever someone worse than him is given more importance by the Father, just like the younger son is given importance by the father.
The prodigal on/the younger soon is the example of a lost sinner who, in his greed and stubborn nature, went on his own. Even then, his father did not abandon him, just like God is with us. After making mistakes and living his life, completely forgetting his creator and father, he lived life as if he's invincible. But once things get bad and he lost everything, he came back, regretting his actions and even ready to be treated like a slave as long as he's forgiven.
At times, even I have acted like the prodigal son. Living life on my own terms and not caring about other stuffs, but then there will always come a time when everything will come to an end. So, in the end, there is only God who will be there with us, never judging or complaining.
The story of the Prodigal Son is the perfect example to show the goodness and forgiving nature of our God. He will never hold a grudge against anyone or his actions. as long as we have the courage to ask for forgiveness, he is willing to welcome us back to the fold.
