He became obedient unto death

It is perfectly legitimate, and, for some purposes it may be useful, to distinguish between the active and passive obedience of Christ, as constituting together his one entire righteousness, and also between the pardon and acceptance of the sinner, as constituting together the one entire privilege of justification.

We are naturally led, even, to make use of such distinctions, in order to illustrate the relation which the constituent elements of Christ's righteousness, and also those of our own justification, bear respectively to the penal and preceptive requirements of the divine Law; but we should ever remember, that two things which are distinguishable in idea, may be inseparable in fact.

It will be found impossible to separate his atoning death from his holy obedience, so as to admit of the one being imputed without the other; for his death was the crowning act of his obedience--"He became obedient unto death, even the death of the cross."

James Buchanan, The Doctrine of Justification, p. 333