If we go back to the book of Genesis we find that after Adam and Eve incurred the debt in question, the first sacrifice took place. "The Lord God made garments of skin for Adam and his wife and clothed them." Genesis 3:21. Without specifying how to perform the ritual, that would come later, a critter or two must have been offered up to provide the garments of skin for the "sinners". Blood was shed, and in so doing, the sin itself was covered with the animals hide. Not removed permanently , or atoned for fully, merely concealed until it showed itself again. Sacrifice must have caught on because we have historical evidence that numerous ancient cultures practiced it, going beyond the use of animal blood to that of humans. So, why blood? Even ancient folks knew that life ebbed away when blood left the body. Life was precious, blood was what sustained life, hence it was the most valuable thing they could offer to appease their gods. Perhaps the element of removing sin was not at the forefront, but placating god, and receiving his protection and blessings were. God knew that people were familiar with sacrifice, and the idea of placing his own son on the altar would catch their attention. Does this seem harsh, primitive and mafia-ish, let's be honest, YES! Did Jesus ask for a defense attorney, or sin accountant to find some kind of loophole for him? Satan offered his services, but Jesus with scriptural authority, dismissed him. "No one can take my life from me. I sacrifice it voluntarily." John 10:18. Does that sound like the basis for an insanity plea, well, YES! Not that he was looking forward to the cruel cross, but being one with the Father, he knew it was the only acceptable course. God could have used someone or something else, but he didn't, remember it was his mind in Jesus, and his blood that flowed through his veins. He choose to prove his love, by paying the debt and sacrificing himself!
I'll be honest, I don't understand it all, and I sure don't have all the answers,but I have faith. Everyone of us puts faith in all kinds of thing we don't fully comprehend. I eat food that I didn't grow, could I get sick, sure, but I trust the producers. I'm getting on a Boeing 777 and flying 3500 miles to London, and yet I can't tell you exactly why that humongous craft stays in the air, but I trust that the pilot and engineers know. We put ourselves in life and death situations on a daily basis. Heck, just driving my Toyota takes a certain amount of faith. To be honest, I haven't studied up on about any of these examples, I blindly trust. Is that intelligent? Probably not, my faith in them is based on the reports of others, some blind like I am, and some informed. The point is, I've studied way more about Christianity than I have aeronautics, and I still don't understand it all, but I have faith that God does, so I choose to believe. Just like getting on that airplane, I trust that God will get me to my final destination. And let's not forget, Jesus may have died on that cross, but he didn't remain in the grave. There in, for me, is all the proof I need.
That outstanding debt is now paid in full, removed once and for all for those who put their faith in that shed blood, no matter how cruel, unjust or pervy it may sound. I can't change anyone's mind, that's God's area of expertise, and crazy as it may seem to those looking in, I choose to trust his method.