How would you explain that God cannot justly overlook sin? Consider this hypothetical conversation:
Q: Why can't God just forgive without a need for a blood sacrifice?
A: He is infinitely holy and just, and his justice must be satisfied before he can justly forgive
Q: But we forgive people all the time for sins committed against us without demanding retribution. In fact it's considered virtuous to do so.
A: We are sinful creatures undeserving of any good thing. But God is holy and sinless, and sins against him are of infinite offense. A good judge will not let prisoners go free without justice first being served.
Q: Yes, but a human judge must uphold justice because he acts on behalf of the one offended. It would indeed be unjust for him to let the criminal go free with no justice for the offended party. But God himself IS the offended party. When I am offended, even as a sinful creature, I can choose to seek justice against the offender, or I can unilaterally choose to overlook it, forgive the offender, and forego seeking his punishment. Why can't God do what I can do?
A: Because God's justice is perfect, and ours is not. Therefore he cannot forgive without his justice being satisfied.
Q: So, does that mean our forgiveness of others without requiring retribution is actually a FLAW in our character? A sign that we are less just than we ought to be? Because if we were more just, we would require a penalty to be paid?
How would you answer this exchange? We assert that God MUST punish sin, but that for man it is considered kind to overlook sin even without retribution and not always demand justice.