The resurrection is the ground of justification
Had Christ succumbed to the death of the cross, that would only have indicated that his union of God and man was not real, that it had not actually been achieved, and therefore that the ethical or legal relation, with its gap between the ‘is’ and the ‘ought’ and its order of distance from God, still stood valid and therefore that every moral or other objection in regard to it was valid. Had Christ succumbed to the death of the cross, its substitutionary sacrifice would have been the most immoral deed in all the universe and, and the only doctrine that would be got out if would be the pagan idea of humanity placating an angry god by human sacrifice. That is partly why Paul lays such stress upon the resurrection as the ground of justification. He speaks of Jesus being put to death for our trespasses and raised for out justification [Rom 4.25], and asks rhetorically, ‘who is to condemn? It is Christ Jesus, who died, yes, who was raised from the dead’? [Rom 8.34] It is because of this resurrection out of the death of the cross that God and humanity have been reconciled in Christ, and therefore that our life has been set on a wholly new basis. (Thomas F. Torrance, Atonement: The Person and Work of Christ, ed. Robert T. Talker [Downers Grove, Ill.: IVP Academic, 2009], 127-28)