Atoning sacrifice is the NIV's translation of a controversial term. It refers to the top of the Mercy Seat on the Ark, but it also refers to what actually happened on the cross. Propitiation emphasizes that God's wrath again sin was appeased, and expiation emphasizes that human guilt was removed.
When the RSV translated the Greek word group as expiation, it was interpreted as a movement toward liberal theology. Today, many see that Jesus' death on the cross (as a physical place, the mercy seat) not only assuaged God's holy and just anger against human sin (propitiation) but it also made it possible for followers of Christ to live without guilt (expiation).
Elements of the Atoning Sacrifice are: