You're right, the explanation of the contradiction is poor. The true contradiction is that your definition of sin is arbitrary -- if God simply decides what is

You're right, the explanation of the contradiction is poor. The true contradiction is that your definition of sin is arbitrary -- if God simply decides what is "sin" and that definition is in and of itself malleable, what makes an action "sinful?" Tomorrow I will see if I have my Socrates texts. I think he spoke about this in the Creeto (piety under the Gods).