In the parable of the prodigal Son..
it is a most curious thing... since the 2 preceeding parables are about a lost coin and sheep... but then those remaining with the 'owner' are those 'who have no need of repentance'
I suggest that in the prodigal son - neither son is a son
the prodigal refuses his sonship, rejects his inheritance and goes to become an orphan
the remaining son, denies his sonship, and insists on being treated like a servant - "where are my wages, boss"
Thus in the parallel - the tax collectors and prostitutes are the lost son, and the pharisees and scribes the son-servant
in another parallel - the Gentiles are those pigs lost to their own pleasures, and the Jews the servants (Gal 4) who refuse the adoption as sons
Therefore to be a true son, born by natural birth, but born by adoption - spiritual birth, but must be received into sonship - in either way - one must come into the loving arms of the Father that dearly cares for both...