Luke 15:21

“And the son said to him, ‘Father, I have sinned against heaven, and in your sight, I am no more worthy to be called your son.' ”

No doubt very moved the son began to explain why he had come. He acknowledged that he had sinned against both God and his father, and that in such a way that he could not expect to be received as a son. That much he had to say in the parable lest the impression be gained that his sin did not matter. But not more, in order to demonstrate the father's unconditional love.