Stated simply, atonement refers to the act by which someone or something is cleansed from sin.
The concept is first introduced in reference to the installation of the priesthood and the consecration of the tabernacle for Israel’s worship (see Exodus 29:35-37).
Atonement is then applied to the rest of the nation when God institutes the Day of Atonement (Yom Kippur) in Leviticus 16. This is the day every year when, through animal sacrifices and a scapegoat, the high priest would symbolically cleanse the priests and tabernacle from the defilement of sin, and then do the same for all the people of Israel.
As the storyline of Scripture progresses, we begin to hear of a greater atonement that God is preparing for his people, one that will fully and finally deal with sin and be eternally effective (see Ezekiel 16:59-63). We see in the New Testament that this sacrifice is the death of Jesus Christ.
The author of Hebrews links the death of Christ to the old covenant concept of atonement, and then shows how much greater Jesus’ sacrifice is:
Every priest stands daily at his service, offering repeatedly the same sacrifices, which can never take away sins. But when Christ had offered for all time a single sacrifice for sins, he sat down at the right hand of God, waiting from that time until his enemies should be made a footstool for his feet. For by a single offering he has perfected for all time those who are being sanctified. (Hebrews 10:11-14)
The glory of Christ’s atonement is that it is no longer limited to a particular nation (Israel) or location (the tabernacle) and neither is it merely symbolically represented through animal sacrifices. By his own blood Jesus has reconciled us to God genuinely and forever, and he holds out this reconciliation to all who trust in his sacrifice on their behalf.