Mark goes into a shop and buys a refrigerator. Why does he do that? Obviously, because, he wants the refrigerator. He agrees with the merchant to pay for the refrigerator and the merchant will deliver it. If Mark has paid the price for it, having examined the refrigerator so as to know what he was buying and that what he is buying was worth the price he paid, does the merchant need to worry that Mark will not accept it once delivered? Not at all; the merchant knows that it is his business to get the goods to the purchaser, in this case Mark, as soon as possible. Again, Mark is expecting the refrigerator to be delivered. If the merchant does not deliver the refrigerator to Mark, the merchant is guilty of fraud. Any buyer, Mark included, will not indifferently say, "Well, I have done my part, and if he doesn't care to do his, he need not—that's all; he may keep the things if he wants to." No; he will visit the shop, and inquire, "Why have you not given me what belongs to me?" He will take vigorous measures to come into possession of his property.
Let us say the merchant is really a criminal that abducted the man's child. This abductor wants fifty thousand dollars in exchange for the man's son. Why does the father pay the $50,000? Because he wants his son back and probably thinks his son is worth more than that. So when he pays the $50,000 the father expects the criminal to keep his word and his side of the bargain: that is to release the child back to his father.
In this case the money paid is called ransom. A ransom is a consideration paid or demanded for the release of someone or something from captivity. It is associated to the word redeem. There are differences between the two however. Although redeem and ransom both mean to buy back. Redeem is wider in its application than ransom, and means to buy back, regain possession of, or exchange for money, goods, etc.; for example, to redeem one's property. To ransom is to redeem a person from captivity by paying a stipulated price; for example: to ransom a kidnapped child. Spiritually, to ransom is to redeem from sin by sacrifice.
Since slaves are held against their will, they are also captives. So, a ransom must be paid to free slaves. In John 8: 34 Christ told the Jews, "…everyone who sins is a slave to sin." Since, we are all sinners, and therefore Sin, we are all slaves to Sin. This concept of slavery to Sin is found in the Old Testament when the Ten Commandments were read, both readings in Exodus and Deuteronomy make reference to it, "I am the LORD thy God, which have brought thee out of the land of Egypt, out of the house of bondage" (Exodus 20:2; Deuteronomy 5:6). The ransom paid for their freedom was symbolically the blood of Christ, since they sacrificed a lamb and put the blood on the door posts (Exodus 12: 3 – 7). Since we are all slaves to Sin, then it follows that we are all in need of redemption. What was symbolically done in Egypt, we all need literally. How can we be set free? Christ said that the Truth sets us free (John 8:32), and the Truth is Jesus (John 14:6). Jesus is the ransom, "… the Son of man came … to give his life a ransom for many" (Matthew 20:28).
At the cross, Jesus paid by His death, the ransom for our souls; a ransom that was full, complete, and once and for all. If Jesus by His death pays the ransom for our souls, then He must be expecting to receive the product He paid for. After all, what good is paying a ransom if you don't come and get what was ransomed? The paying of the ransom isn't the end of the story. Just as a human parent would come get the child he or she ransomed back, so, too, Jesus will come back to get what He paid such a great price for. Hence, Christ's first coming gives us the greatest assurance possible for the second. He wants to have in His possession what He purchased.