The most ancient theory is often called the 'ransom' theory. This view says that we humans, through our sin, placed ourselves under the authority of Satan." I didn't notice that Kerry squirmed when I said "Satan," but Carol told me later that she did. "Jesus comes and offers himself as a ransom for us. He says to Satan, "If I give you myself, will you set them free?' Satan agrees to the bargain, and so he takes, tortures, and kills Jesus, whose self-sacrifice sets us free. Of course, in the end, God double-crosses Satan--pardon the pun--by raising Jesus from the dead. So Satan is double the loser, and we're set free to live for and with God again."
Mark 10:45 -- For even the Son of Man did not come to be served, but to serve, and to give his life as a ransom for many.”
1 Timothy 2:6 -- For there is one God and one mediator between God and men, the man Christ Jesus, who gave himself as a ransom for all men—the testimony given in its proper time.
According to this site, this theory was the earliest in Christian history. It is bothersome because God seems deceitful.
CS Lewis preferred another theory, but this theory is similar to what he used in Lion, Witch, and the Wardrobe. In the book, a deep magic from the dawn of time says that a righteous one's death can free a traitor from the clutches of the White Witch. What she doesn't know is that a deeper magic from before the dawn of time says that when that happens, death will reverse itself. So she isn't so much deceived, as surprised.
Other problems are "Why should God have to pay Satan?" This theory certainly makes Satan the main problem.
So asking Brant's question, who did this forgive? Perhaps this is a question that directs itself to all of the theories. But I think I'll wade through the theories first.
My Millard Ericson Christian Theology seems to be misplaced (or not returned). Though he sees differently, he is a very clear writer, unlike Oden and Dunning, whose books are still on my shelf.