If I were to get pulled over for speeding, I could not get away by telling the police officer to give my ticket to someone else. As the one who deserves the penalty, I am in no way authorized to suggest a transference of that penalty. Likewise, in a human court of law, the judge cannot sentence an innocent person for the crime of the guilty party. That is not within his domain of authority. The state has authorized him to try cases and mete out appropriate punishments, but since he is neither the offended party or the one who makes the laws that he enforces (I guess we're not talking about Supreme Court justices here), he cannot simply reassign just penalties wherever he likes. The situation is a lot different when I'm the offended party. If someone harms me or my property, I have a right to either press charges or not, but I still don't have the right to shift who I press the charges against. If one person steals my television, I can't insist that someone else take the blame. That is because I have not been wronged by the other person, and so it would not be just to swap the penalty. Also, I'm not the one who has made the law, so I can't change how the penalties are carried out. I'm under someone else's authority on this matter.
God does not operate under these considerations, however. That is simply because He is the One who has both crafted all of the laws and the One who has been offended by the breaking of those laws. All of the authority to decide what ought to be done at that point belongs to Him. As the Owner and King of everything, He can do whatever He wants with His property.
I was reminded of this as I read Numbers chapter 3 this morning. When God freed the people of Israel from their slavery to the Egyptians, He told them that all of their firstborn males would be devoted to Him. This was because God had killed all of the firstborn of Egypt, but spared the Hebrews. So, instead of killing the Hebrew children, He demanded that they be devoted to Him and then redeemed by a sacrifice in their stead. As the Lawmaker, He could demand an animal sacrifice in place of a human death. And then in Numbers 3:11-13, He declared that all of the males of the tribe of Levi would be His instead of the firstborn males from the other tribes. He switched out the requirement again, and once again He had every right to do so because He made the requirement in the first place, and all of those who were affected belonged totally to Him since He had "bought" them by saving them in the Exodus.
And of course, this is exactly what happened at the cross in the death of Jesus Christ. Since God is the One who made the laws that were broken by sinful humanity, He, as the offended party, has the both the right to dictate the terms of the punishment and the right to call for a substitute to receive the penalty if He so desires. The only other consideration is that since God is perfectly just, the penalty that is meted out must not be lessened or redundant with some other penalty. All just penalties must be fully endured for the sake of justice. In other words, He couldn't just double up the penalty on one who is already guilty in order to redeem somebody else. You can't set one murderer free by killing another murderer twice. Justice would not be done.
So the penalty must fall on One who does not deserve a penalty on His own. But if there was such a person outside of God Himself, then God would be unjust in transferring the sins of disobedient humanity to that one. No, the only solution is for the Judge Himself, the offended party and the Maker of the laws, to accept on Himself the punishments for the disobedience of His own rules. If He has to be just and He wants to redeem the guilty, then this is the only choice. And so Christ, the eternal Image of God - His manifestation - took on mortal flesh to be able to receive the blow from God's wrath that we deserved. It is simultaneously the infinitely perfect display of love, justice, mercy, wrath, righteousness, and grace. Hallelujah! What a Savior!