The Atonement...Simply Put

The atonement is the completed sacrificial work of Christ in His life and death to satisfy the Laws demands unto God the Father. The atonement deals with the problem of sin, so that in mercy, fallen mankind might be restored to a relationship with God. It literally means at-one-ment; what was done so we might be at one with God.
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Why was this needed? In the Garden, Adam and Eve needed to obey the Law, or Covenant of Works (Gen 2:15), or face the consequence/wage. The Law demanded perfect obedience (righteousness) or the wage/consequence would be perfect justice (Ro 6:23a). In breaking the Covenant they died spiritually and began to die physically. They were cut off from God and under His wrath.

Grudem defines the atonement simply as, “The work Christ did in his life and death to earn our salvation.” (Grudem, Systematic Theology, 1236; c.f. 1689.8.4).

Since we were: a) disobedient, and b) are under just sentence, Jesus’ atoning work had a twofold nature to it: His active obedience and passive obedience.

• Active obedience: Jesus lived the perfect life, the life we should have lived (Phil 3:9; Mt 3:15; Ro 5:19; 2 Cor 5:21, etc). He was perfect as a child, perfect in temptation, perfect in ministry, perfect under the Law, perfect in suffering and death. In this He ‘fulfilled righteousness’ and the Father accepted His perfect life and fulfillment of the Law as righteous.
• Passive obedience: In His suffering and death, Jesus paid the punishment and final penalty for breaking the Law, for sin, which was suffering and ultimately death. Jesus suffered in leaving heaven, He suffered in living amongst sinners, He suffered when He was tempted, He suffered when His family wouldn’t believe in Him and when He was rejected, He suffered the loss of friends, He suffered betrayal. Finally, in Gathsemane as He sweat blood (not merely because of what He would face but what He received [the sentence of sin deserved]), He took the penalty of sin and bore it to Calvary through His Passion (suffering). He further suffered abandonment (God and friends), arrest, injustice, scourging, mockery, jeers and crucifixion, where the full wrath of God toward sin was poured out upon Jesus until complete payment/satisfaction was made to the Father, until He died (blood). He was a man of sorrows (Isa 53:3) who made atonement for sin (again 2 Cor 5:21, Ro 3:25, 1 Pe 2:24, etc).

The atonement, both Jesus’ active and passive obedience, fulfilled the Laws demands unto the Father such that in Christ, the Father would accept His substitute for the believer. Jesus did the work that was needed so that at-one-ment could be made. Faith is how we access these benefits. By faith, Christ’s active obedience (righteousness) is imputed/credited to our account. When the Father sees us, He now sees His Son’s perfect righteousness. By faith, our sin/unrighteousness is credited to Christ, such that because of His death/penalty, we can go free, forgiven, our account cleared. Both are needed to be at-one with God, otherwise we could be forgiven but not fit for heaven, etc.

Atonement is what Christ did. Justification by faith is how the sinner accesses Christ’s merits to be declared just, or righteous (both morally and legally).
 
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