"Imputation is more than central; it's essential to the New Testament gospel. Friends, I beg you never to negotiate the concept of the imputed righteousness of Christ. That's the article upon which we stand and fall because without His righteousness all we have to offer God is filthy rags ... The righteousness by which we are justified is an alien righteousness - a foreign righteousness. If this expression is unclear to you, know that Luther also described justification as a righteousness that is outside of us, apart from us.
The only righteousness that will justify us is the righteousness of Christ. We are naked and helpless without the cloak of His righteousness covering us. We are foul in God's sight until He imputes to us the righteousness of Christ".
R C Sproul - "Preaching the Cross" - Crossway Books, Illinois (2007) - (p97-98).