Is it true that Roman Catholicism teaches salvation by works, whereas Protestantism teaches salvation by faith alone?
No, that is not quite true. In fact, a statement like this is slanderous to Roman Catholics. To understand the key difference between Roman Catholicism and Protestantism and so to appreciate the key issue of the 16th century Reformation, we must first begin by using more precise theological terms. The word “salvation” is a very broad term which covers not only conversion, which happens when a person becomes a Christian, but also the Christian’s life of growing in faith, love and holiness (sanctification). Thus, when Paul tells us to “work out your own salvation with fear and trembling” (Phil 2:12), he is referring to our sanctification. When the term “salvation” is used in this sense, it would be misleading to say that Protestantism teaches salvation by faith alone.
Moreover, when “salvation” is used in this sense, we would not quarrel with Rome’s teaching that works is necessary for salvation—though we will insist that works is not meritorious.
The great divide between Protestantism and Catholicism, however, concerns the instrument or means by which justification is applied to the sinner so that he may be reckoned as righteous and forgiven in the sight of God. Our question becomes more meaningful when the word “salvation” is replaced with “justification.” But it is still incorrect to say that “Roman Catholicism teaches justification by works.” More accurately, Roman Catholicism teaches “justification by faith plus works.” The difference between the Roman Catholic and the Protestant doctrine of justification by faith may be illustrated in the following formula devised by John H. Gerstner:
We see that Protestantism or Biblicalism teaches that justification is by faith alone, but that faith is not alone, in that it produces good works which are acceptable to God through Christ by justification. In biblical doctrine, justification is a reckoning or imputing of the righteousness of Christ to the elect with the result that the wrath of God is turned away from him. Justification is sealed to the elect when he believes in Christ and is received by God as a prodigal son. Thus faith may be said to be the hand that receives justification. Works, on the other hand, is not a pre-requisite but a post-requisite for justification (cf. Rom 1:17; 5:1–3; 11:6; Eph 2:8–10. Note also that good works verify rather than sanctify, cf. WCF 13.1, 16.2).
Rome, however, teaches that justification is an infusing of righteousness into the believing worker who thereby becomes intrinsically (actually) righteous. The Roman Council of Trent teaches that faith is the radix or root of justification, and faith must automatically lead to good works (which we agree). But Trent goes on to teach that the good works become the title to eternal life. That is, through faith in Christ (which is not itself saving), the believer is enabled to achieve his own justification by works and so attain eternal life. But there are three problems with this view. Firstly, it denies the sufficiency of the atonement of Christ, for additional work is required for justification. Secondly, it over-estimates the perfection of the work and obedience of unglorified man, since God cannot accept works tainted with sin (which was why Christ had to live and die on our behalf). Thirdly, it makes God obligated to reward obedience and good works of His creatures (however perfect it may be), when the Scripture teaches that it is man’s obligation to be obedient and to do good (Lk 17:7–10).
The Romish error of justification leads to a whole plethora of errors, including Indulgences—the buying and selling of excess merits of saints who had done more good works than sufficient in their lifetime to secure their own salvation.