Jesus’ so-called “passive” and “active” obedience were lifelong endeavors as he fulfilled the demands and suffered the penalties of God’s law, and both culminated in the cross.
Though some critics of Reformed theology critique the distinction as extrabiblical, I think the New Testament clearly teaches both aspects: the lifelong passive obedience of Christ (his penalty-bearing work of suffering and humiliation) and the lifelong active obedience of Christ (his will-of-God-obeying work) culminate in the cross. Those who trust in him and are united to him do not just have his active obedience credited to their account; nor do they just have his passive obedience credited to their account. The Bible doesn’t divide his obedience up in this way. Rather, believers are recognized as righteous through the imputation of the whole obedience of Christ (the reckoning of Christ’s complete work to our account).
In other words, confessionally Reformed folks argue for both-and, not either-or. In the New Testament, Christ’s righteous work is of one cloth: it’s always “obedience unto death.” One cannot separate Christ’s fulfillment of God’s precepts from Christ’s payment of the penalty for our failing to obey God’s precepts.
– Justin Taylor