A Trinitarian understanding of the Atonement

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In Faith Seeking Understanding, Daniel Migliore summarizes and critiques the three primary theories of the Atonement in classical Western theology. Why more than one? Largely because the New Testament uses several metaphors to describe the Atonement, and each theory tends to focus on one, sometimes at the expense of the others. Here is a summary of each theory:

1. Christ the Victor theory, which develops the NT's battle metaphor (e.g. Col 2:15). Migliore comments:
According to this view, the work of atonement is a dramatic struggle between God and the forces of evil in the world....Under the veil of his humanity, Christ triumphs over the demons, the devil, and all the principalities and powers that hold human beings captive. By his cross and resurrection, Christ decisively defeats these powers an thus frees their captives (pp. 182-3).
 2. Anselm's Satisfaction theory, which arose in the medieval period. It emphasizes scriptures that suggest that humankind is redeemed by Jesus' vicarious suffering on our behalf (e.g. Isa 53; Gal 3:13). This theory tends to see the Atonement as a legal transaction in which God, like a feudal lord, deals with humans as though they are his serfs. Migliore comments:
Since disobedience dishonors the lord, either satisfaction must be given or punishment must follow. The satisfaction that is due to God on account of the offense of [human] sin is infinite. While humanity must provide this satisfaction, only God can provide it.... For this reason God has become human in Christ. In his perfect obedience unto death, satisfaction is rendered, justice is done, God's honor is restored, and sinners are forgiven (p. 184). 
3. Moral Influence theory, which emphasizes that Christ...
...shows God's love to us in such a compelling way that we are constrained to respond in wonder and gratitude. The atoning work of Christ [therefore] is complete only when it is appropriated in the act of faith and allowed to transform one's life" (Migliore, p. 185).
As Migliore notes, though each theory offers valuable insight concerning the nature of the Atonement, each, in itself, is incomplete - leaving behind something of the full riches of the person and work of Christ revealed in the gospel.

For Migliore (after Barth), to be faithful to Scripture, one's doctrine of the Atonement must include a full and faithful understanding of who Jesus is as prophet, priest and king (not just one these roles). Moreover, it must uphold the foundational truth of Jesus' full divinity and full humanity. These truths are carefully upheld in a Trinitarian-incarnational doctrine of the Atonement that...
  1. Respects all the NT metaphors concerning the Atonement.    
  2. Encompasses the full gospel story (unlike, for example, the satisfaction theory, which tends to focus on Jesus' death). Indeed, all of Jesus' vicarious (representative/substitutionary) conception, life, baptism, ministry, suffering, death, burial, resurrection and continuing intercession, is fundamental to the Atonement.
  3. Emphasizes that atonement is based on God's gracious initiative, even while it understands the importance and place of human response.
  4. Understands that "the grace of God includes judgment, and the judgment of God serves the purpose of grace. A doctrine of atonement should not present the grace and judgment of God as conflicting with each other" (p. 187).
  5. Recognizes that "the atoning work of God in Christ has significance for individuals, society, and the entire cosmos" (p. 187).