Convinced that "Paul's fullest, grandest, most comprehensive statement of the gospel" is just as vital today, R.C. Sproul delivered nearly sixty sermons on Romans at St. Andrew's Chapel. These never-before-published expositions are now available in a hardcover book comprising over 500 pages of material. More information available here.
"The glory of his grace is that his justice is served vicariously by a substitute that he appointed."
God set forth Christ as a propitiation by his blood through faith that He might be just and the justifier of the one who has faith in Jesus (Rom 3:26). There is no such thing as cheap grace. The gospel is not simply an announcement of pardon. In justification God does not merely decide unilaterally to forgive us our sins. That is the prevailing idea, that what happens in the gospel is that God freely forgives us of sin because he is such a loving, dear, wonderful God, and it does not disturb him that we violate everything that is holy. God never negotiates his righteousness. God will never lay aside his holiness to save us. God demands and requires that sin be punished. That is why the cross is the universal symbol of Christianity. Christ had to die because, according to God, the propitiation had to be made; sin had to be punished. Our sin has to be punished.
In the drama of justification, God remains just. He does not set aside his justice. He does not waive his righteousness; he insists upon it. We cannot be justified without righteousness, but the glory of his grace is that his justice is served vicariously by a substitute that he appointed. God’s mercy is shown in that what saves us is not our righteousness. It is someone else’s. We get in on someone else’s coattails—that is grace. That somebody, our Redeemer, is perfectly righteous and has fulfilled the justice of God for us perfectly. That is the glory of justification. God demonstrates that he is both just and justifier. If all he did was maintain his righteousness without extending the imputation of that righteousness to us, he would not be the justifier. He is both just and justifier, which is the marvel of the gospel. (pp 104).