Dr Ferguson quoted John Murray in his commentary on Romans thus:
It should be noted in addition that the apostle conceives of this redemption as something that has its permanent and abiding tenancy in Christ; it is "the redemption that is in Christ Jesus". The redemption is not simply that which we have in Christ (Eph. 1:7) but it is the redemption of which Christ is the embodiment. Redemption has not only been wrought by Christ but in the Redeemer this redemption resides in its unabbreviated virtue and efficacy. And it is redemption thus conceived that provides the mediacy through which justification by God's free grace is applied.