Heidi's grandfather quotes from the story of the Prodigal Son in the Gospel of Luke. He uses the words spoken by the son when he returns home and asks for his father's forgiveness.
The relevant passage of the Prodigal Son in the King James Version of the Bible reads:
And the son said unto him, "Father I have sinned against heaven, and in thy sight, and am no more worthy to be called thy son." (Luke 15:21).
In the English Standard Version of the Bible (2001), the passage is:
His son said to him, "Father, I have sinned against heaven and before you. I am no longer worthy to be called your son."