[P]utting the atonement exclusively in a legal context misses the essence of "covenant" . . . If one party breaches the terms of the covenant, the other party still loves the offender and is bound to show him mercy. In a legal arrangement, there is no provisions for love, concern, or forgiveness. A criminal defendant is convicted or freed based upon the letter of the law, not the love and mercy of the judge. In the New Covenant, Christ's atoning work is an act of gracious mercy, not legal acquittal. This is why Paul tells the Romans: "You are not under law but under grace" (Rom 6:14)
Second, if the penal substitution theory were true, God would legally owe us salvation, and no one would go to hell. That is because God, being perfectly just, would not require two payments for the same sin. We know that this cannot be true, however, because Jesus said people would go to hell. In fact, if Christ paid the eternal penalty for our sins, He would be suffering in hell for eternity. Thus, the Protestant doctrine of "penal substitution" is nothing more than a theological fiction.
Protestants may counter by saying that Jesus' payment for our sins is effective only when a person accepts that payment in faith. However, if the Atonement were purely a legal transaction, then faith would not be required at all, because faith is not a dimension of law. (A convicted criminal's faith in his sentencing judge has no bearing on the prison term he receives). Rather, faith is a dimension of covenant relationships, particularly within the context of family. Hence, Christ's Atonement is not an impersonal legal motion to a judge to pardon a criminal, but a personal plea to the Father to forgive the sinner. Christ doesn't free us like defendants from prison, but reconciles us as sons and daughters to our heavenly Father. The Atonement is about personal propitiation, not legal pardon. (John Salza, The Biblical Basis for the Eucharist [Huntington, Ind.: Our Sunday Visitor, 2008], 43-44)