No unclean thing can enter into the presence of God (see Rev 21:27). The payment is not due to a person, it is due to the concept of justice. If you sin, justice demands that you be excluded from the presence of God. Jesus was punished for sins he never committed. That was unjust. To satisfy justice, God ceded the right to extend mercy (not being punished for something you did do) to Jesus. Jesus has the right to forgive sins committed (mercy) and return you to the presence of God. You still have free will. You can accept the forgiveness or go your own way. Unlike the retail stores, this one doesn't come with a 30 day free trial. You have to make the decision for yourself.
"No unclean thing can enter into the presence of God (see Rev 21:27)."
Contra:
Jesus was God (Gospel of John).
Unclean things were all about him, all the time.
Adam and Eve sinned, and God came and talked to them before casting them out. They were unclean, but in God's presence.
At any rate, the Bible does not bind God.
Revelation states "No unclean thing can enter into the presence of God." But if that is so, it is only because God chooses it to be so. He is God, He need not have it so. He chooses it to be so, and demands that it be so, and therefore demands that sins be paid...including by the sacrifice of His innocent Son. It was not NECESSARY that this happen, because nothing is required of God. God CHOSE for this to happen (assuming that our theology is actually correct). Which means that the reason that sin needs to be paid for is because God says so, and he says so because He feels like it, because by definition nothing can bind God, so there is truly no "necessary" with God.