How Can I Be Right With God by R.C. Sproul
The Christian Faith has some teachings that are indispensable for one to be considered "A Christian Biblically." One of the most important questions that anyone can wrestle with is, "How can I, a sinful unholy creature, be reconciled to my Maker, who is a Thrice Holy God?" A correct understanding (that is to say, an accurate Biblical comprehension) of Justification by Faith Alone is (as Sproul puts it), "no mere academic issue". It is a matter of life and death, a matter of eternal life and eternal death. The Doctrine of Justification concerns Man's greatest need——"The Doctrine of Justification addresses the solution to that problem, declaring how we, as unjust people, can be reconciled to a just and Holy God." If you build a structure without a good foundation, it will not last long, (It will eventually crumble to the ground) that is what Justification is to the doctrine of salvation.
In chapter four, "The Great Exchange," Sproul considers an essential aspect of every man's justification, the concept of —"In Justification, two kinds of imputation take place. There is the imputation of The Righteousness of Christ To Us and the Imputation of our sin to Christ." Without imputation, there cannot be a Gospel that saves hell-deserving sinners from the wrath of Almighty God. Perhaps the clearest verse in the Book of God on the great exchange which takes place is 2 Corinthians 5:21: "For He has made Him to be sin for us, who knew no sin, that we might be made the righteousness of God in Him." What a glorious truth this is! That is why that man or woman is blessed because God has nailed their sin to the cross of their crucified Savior.
R.C. expresses concern that those who contend that the Roman Catholic Church doesn't believe in "Justification by Faith" are not accurately representing what they do in fact believe and teach about Justification by Faith. Sproul astutely contends that, ". . . what's missing in the Roman Catholic formula regarding faith is the word, Sola." It is not faith (as a work of some kind) that saves an individual but faith is the channel or bridge "to the Righteousness of Christ" being imputed to us. The Roman Catholic view is that of infused grace, the person actually becomes more righteous "in themselves" (and this is a part of their justification) thus justification is synergistic, as opposed to "an Alien Righteousness" (the righteousness of another that is given to them through faith).
This has long been one of my favorite books in The Crucial Questions series. In part because it is such a great handout for unbelievers and for those who may be "seeking God" as well.