Atonement means at-one-ment.  Atonement restricted only to the cross always leads us astray with inadequate plans of salvation.  The atonement starts in the incarnation and includes the life He lived, the death He died, the burial He underwent, the resurrection He experienced, the ascension back to the Father, His enthronement in heaven at the right hand of His Father, sprinkling the heavenly mercy seat with His blood and His present intercession for us.  These are all necessary and essential pieces of the atonement.  All of these together make our at-one-ment with God.  He accomplished this at-one-ment by being at-one with us and us being at-one with him.

“God was in Christ reconciling the world to Himself,…so that we might become the righteousness of God in Him.” 2 Corinthians 5:19, 21 (NASB)