The Keeper of the Underworld hungers for all living souls, but you, a child born of a War Wizard and a Mother Confessor—then artificially aged by the Boxes of Orden—is essentially a 'flaw' in the metaphysics of life and death. Because you were 'grown' by the magic of the Underworld - Subtractive Magic - but possesses the spark of the Creator - Additive Magic -, you exists in a state of permanent tethering between both realms.
The Keeper doesn't see you as a servant; he sees you as a gateway. Usually, the Keeper needs 'Agents' or 'Sisters of the Dark' to tear the veil. You are the tear. Every breath you takes, because your growth was unnatural, pulls the underworld closer to the world of the living. The Keeper whisper to you in your dreams, offering you the one thing Darken Rahl cannot: a true identity. He would promise to take away the 'noise' of the living and give you the silence of eternity, the true peace.
Even though Darken Rahl raised you to be a monster, you inherited Richard’s heart and his 'Seeker' soul. Deep down, you cannot help but seek the truth of your own existence. You might realize that if you are the Prince of D'Hara', why does you feel like a ghost? You starts to resist the Keeper not because you are 'good', but because you are stubborn. You refuses to be a tool for a god of death or a pawn for a narcissistic 'father'.
To resist the Keeper, you considered using the very subtractive magic he had given you. By beginning to 'eat' the shadows sent to claim you, you'll become a power vacuum that even Rahl would fear.
The boy sat alone in the center of a wizard’s sand-spell, his eyes closed. Around him, the air wasn't just cold, it was oppressive. 'You are mine, little spark.' A voice drifted from the floorboards—a sound like grinding bone and dying breaths. The Keeper was reaching through the veil, his presence a literal weight on the boy’s chest. 'Rahl gave you flesh, but I gave you the time to wear it. Soon you will come home...in the silence...'