For some today, double imputation alone grounds the gospel. If Christ’s passive obedience (death on the cross) alone is imputed, then we are forgiven but not positively righteous. We need to have Christ’s active obedience (in life) imputed if we are to be counted positively as law-keepers, as righteous in God’s sight.
That’s not the way Paul sets things up: Christ was delivered up for our transgressions and raised for our justification (Romans 4:25). We are positively righteous because we are united to Jesus, who is declared righteous in the resurrection.
Perhaps double imputation arises from the assumption that the transaction that secures our standing with God takes place exclusively on the cross.
Perhaps double imputation is compensation for ignoring the soteriological import of the resurrection.