It can be universally said that Jesus died to atone for the sins of Mankind, to absolve us of our sins, and become reconciled with God. The problem is, I think, and the reason why we have so many "theories," how and why the atonement had to be fulfilled in the first place. What I mean is, Jesus had to fulfill something so that sinners could be saved and reconciled with God. Now, the NT repeatedly says that Jesus died as a "ransom for many," and Paul writes were were "bought at a cost." Hence, we see two economic-based terms there.
The Ransom Theory, while outlandish, is only plausible in that Satan had a temporary "victory" against God because Satan's cohorts "won," and Jesus was killed; however, Satan quickly lost, because Jesus was resurrected.
Now, I say fulfill because I feel Jesus needed to fulfill the Law of God, which is why He was sent. Yes, He was sent to save, but also to fulfill the Law of the OT and create a new law. Law and order are needed, so Jesus's death was intended to reinstall order to God's government, which was on the verge of collapse.