What is the doctrine of expiation?
In "Doctrinal Discussion" Randy Bland writes:
The doctrine of expiation says that believers can further be cleansed from the stain of sin.
This doctrine goes back to the time when God gave the law to Moses. Once a year on the Day of Atonement the Israelites were to sacrifice two goats to the Lord. The first goat was to be killed as a sin offering for the people. This sacrifice of propitiation was offered to satisfy God’s wrath. The second goat was treated very differently. The high priest was to lay his hands upon the head of the goat and confess all of the sins and iniquities of the people, thus transferring them from the people to the goat. This scapegoat was then banished from camp and set to wander in the wilderness, forever cut off from the people. He was a sacrifice of expiation that cleansed the people by carrying away their sins.
Jesus was our Scapegoat, taking away our sins so that we could be cleansed from the stain of sin.
Source: Jesus, Son of God: Adult Teacher's Insights, page 20.