Redemption: Deliverance at Cost

In The Apostolic Preaching of the Cross, Leon Morris argues cogently concerning the redemption-language background for the usage in the New Testament. Of this book as a whole, D. A. Carson recently said in a classroom exposition of Rom. 3:21-26 that the book is a "must read." He added, "sell your shirt for it" if you must. And I can see why. 

Here's Morris's summary of that redemption-language background:

We see then, that in Greek writings generally, in the Old Testament, and in Rabbinic writers, the basic idea in redemption is the paying of a ransom price to secure a liberation. Circumstances may vary, for the word applies to the freeing of a prisoner of war, or of a man under sentence of death because his ox has gored a man, or of articles in paw, or of a slave seeking manumission. But always there is the idea of payment of a ransom to secure the desired effect. 

When God is the subject of the verb we noticed a difference, for it is inconceivable that He should pay a ransom to men, and in those passages there tends to be a greater stress on the idea of deliverance than on the means by which it is brought about. Yet even here we saw that the Old Testament writers were not unmindful of the meaning of the words they were applying to God's dealings with His people, for they think of Him as delivering at some cost. Clearly the metaphor was one with point. 

—Leon Morris, The Apostolic Preaching of the Cross (Grand Rapids: Eerdmans, 2000), 29.