A good illustration of the progressive nature of theology is found in the doctrine of the atonement. All of the apostles taught distinctly that Christ died for our sins. The early Christians did not attempt to go behind that fact, but by and by men began to attempt explanations. In the second century a man by the name of Irenaeus seized upon the word "ransom" in the sentence, "The Son of man is come to give his life a ransom for many," and found in that word "ransom" the key-word of the whole problem. The explanation of Irenaeus was taken up in the third century by a distinguished preacher, Origen. And in the fourth century the teaching of Origen was elaborated by Gregory of Nyssa. According to the interpretation of these men, Jesus was the price paid for the redemption of men. Paul frequently used the word redemption, and the word had definite meanings to people who lived in the first four centuries of the Christian era. If Christ was indeed a ransom, the question naturally arose, who paid the price? The answer was, God. A ransom must be paid to somebody--to whom was this ransom paid? The answer was, the devil. According to Origen and to Gregory, God paid the devil the life of Jesus in order that the devil might let humanity go free. The devil, by deceit, had tricked man, and man had become his slave--God now plays a trick upon the devil, and by offering him the life of Jesus, secures the release of man. That was the interpretation held by many theologians for almost a thousand years, but in the eleventh century there arose a man who was not satisfied with the old interpretation. The world had outgrown it. To many it seemed ridiculous, to some it seemed blasphemous. There was an Italian by the name of Anselm who was an earnest student of the Scriptures, and he seized upon the word "debt" as the key-word of the problem. He wrote a book, one of the epoch-making books of Christendom, which he called "_Cur Deus Homo_." In this book Anselm elaborated his interpretation of the reconciliation. "Sin," he said, "is debt, and sin against an infinite being is an infinite debt. A finite being can not pay an infinite debt, hence an infinite being must become man in order that the debt may be paid. The Son of God, therefore, assumes the form of man, and by his sufferings on the cross pays the debt which allows humanity to go free." The interpretation was an advance upon that of Origen and Gregory, but it was not final. It was repudiated by men of the twelfth and thirteenth centuries, and finally, in the day of the Reformation, it was either modified or cast away altogether.