Joachims response is predicated on the favorite sermon of his
foster father Pastor Fuerchtegott Trotz on the verse that he who
looks at a woman lustfully has committed adultery with her in
his heart.  And resolved his dilemma with the conclusion that
what matters is not the biological but the spiritual paternity
as the most persuasive basis of the imitatio Christi. And so he

But I say unto you, That whosoever looketh on a woman to lust 
after her hath committed adultery with her already in his heart.
Matthew 5:28