Is Roman Catholicism Biblical?

     In today's spirit of ecumenism, many evangelicals have called for the Protestant Church to lay aside its differences with Rome and pursue unity with the Catholic Church. Is that possible? Is Roman Catholicism simply another facet of the body of Christ that should be brought into union with its Protestant counterpart? Is Roman Catholicism simply another Christian denomination?
While there are many errors in the teaching of the Catholic Church (for example its belief in the transubstantiation of the communion wafer and its view of Mary), two rise to the forefront and call for special attention: its denial of the doctrine of sola Scriptura and its denial of the biblical teaching on justification. To put it simply, because the Roman Catholic Church has refused to submit itself to the authority of God's Word and to embrace the gospel of justification taught in Scripture, it has set itself apart from the true body of Christ. It is a false and deceptive form of Christianity.
The Doctrine of Sola Scriptura
     In the words of reformer Martin Luther, the doctrine of sola Scriptura means that "what is asserted without the Scriptures or proven revelation may be held as an opinion, but need not be believed." Roman Catholicism flatly rejects this principle, adding a host of traditions and Church teachings and declaring them binding on all true believers--with the threat of eternal damnation to those who hold contradictory opinions.
     In Roman Catholicism, "the Word of God" encompasses not only the Bible, but also the Apocrypha, the Magisterium (the Church's authority to teach and interpret divine truth), the Pope's ex cathedra pronouncements, and an indefinite body of church tradition, some formalized in canon law and some not yet committed to writing. Whereas evangelical Protestants believe the Bible is the ultimate test of all truth, Roman Catholics believe the Church determines what is true and what is not. In effect, this makes the Church a higher authority than Scripture.
     Creeds and doctrinal statements are certainly important. However, creeds, decisions of church councils, all doctrine, and even the church itself must be judged by Scripture--not vice versa. Scripture is to be accurately interpreted in its context by comparing it to Scripture--certainly not according to anyone's personal whims. Scripture itself is thus the sole binding rule of faith and practice for all Christians. Protestant creeds and doctrinal statements simply express the churches' collective understanding of the proper interpretation of Scripture. In no sense could the creeds and pronouncements of the churches ever constitute an authority equal to or higher than Scripture. Scripture always takes priority over the church in the rank of authority.
     Roman Catholics, on the other hand, believe the infallible touchstone of truth is the Church itself. The Church not only infallibly determines the proper interpretation of Scripture, but also supplements Scripture with additional traditions and teaching. That combination of Church tradition plus the Church's interpretation of Scripture is what constitutes the binding rule of faith and practice for Catholics. The fact is, the Church sets itself above Holy Scripture in rank of authority.
The Doctrine of Justification
     According to Roman Catholicism, justification is a process in which God's grace is poured forth into the sinner's heart, making that person progressively more righteous. During this process, it is the sinner's responsibility to preserve and increase that grace by various good works. The means by which justification is initially obtained is not faith, but the sacrament of baptism. Furthermore, justification is forfeited whenever the believer commits a mortal sin, such as hatred or adultery. In the teaching of the Roman Catholic Church, then, works are necessary both to begin and to continue the process of justification.
     The error in the Catholic Church's position on justification may be summed up in four biblical arguments. First, Scripture presents justification as instantaneous, not gradual. Contrasting the proud Pharisee with the broken, repentant tax-gatherer who smote his breast and prayed humbly for divine mercy, Jesus said that the tax-gatherer "went down to his house justified" (Luke 18:14). His justification was instantaneous, complete before he performed any work, based solely on his repentant faith. Jesus also said, "Truly, truly, I say to you, he who hears My word, and believes Him who sent Me, has eternal life, and does not come into judgment, but has passed out of death into life" (John 5:24). Eternal life is the present possession of all who believe--and by definition eternal life cannot be lost. The one who believes immediately passes from spiritual death to eternal life, because that person is instantaneously justified (see Rom. 5:1, 9; 8:1).
     Second, justification means the sinner is declared righteous, not actually made righteous. This goes hand in hand with the fact that justification is instantaneous. There is no process to be performed--justification is purely a forensic reality, a declaration God makes about the sinner. Justification takes place in the court of God, not in the soul of the sinner. It is an objective fact, not a subjective phenomenon, and it changes the sinner's status, not his nature. Justification is an immediate decree, a divine "not guilty" verdict on behalf of the believing sinner in which God declares him to be righteous in His sight.
     Third, the Bible teaches that justification means righteousness is imputed, not infused. Righteousness is "reckoned," or credited to the account of those who believe (Rom. 4:3-25). They stand justified before God not because of their own righteousness (Rom. 3:10), but because of a perfect righteousness outside themselves that is reckoned to them by faith (Phil. 3:9). Where does that perfect righteousness come from? It is God's own righteousness (Rom. 10:3), and it is the believer's in the person of Jesus Christ (1 Cor. 1:30). Christ's own perfect righteousness is credited to the believer's personal account (Rom. 5:17, 19), just as the full guilt of the believer's sin was imputed to Christ (2 Cor. 5:21). The only merit God accepts for salvation is that of Jesus Christ; nothing man can ever do could earn God's favor or add anything to the merit of Christ.
     Fourth and finally, Scripture clearly teaches that man is justified by faith alone, not by faith plus works. According to the Apostle Paul, "If it is by grace, it is no longer on the basis of works, otherwise grace is no longer grace" (Rom. 11:6). Elsewhere Paul testifies, "By grace you have been saved through faith; and that not of yourselves, it is the gift of God; not as a result of works, that no one should boast" (Eph. 2:8-9, emphasis added; see Acts 16:31 and Rom. 4:3-6). In fact, it is clearly taught throughout Scripture that "a man is justified by faith apart from works of the Law" (Rom. 3:28; see Gal. 2:16; Rom. 9:31-32; 10:3).
In contrast, Roman Catholicism places an undue stress on human works. Catholic doctrine denies that God "justifies the ungodly" (Rom. 4:5) without first making them godly. Good works therefore become the ground of justification. As thousands of former Catholics will testify, Roman Catholic doctrine and liturgy obscure the essential truth that the believer is saved by grace through faith and not by his own works (Eph. 2:8-9). In a simple sense, Catholics genuinely believe they are saved by doing good, confessing sin, and observing ceremonies.
Adding works to faith as the grounds of justification is precisely the teaching that Paul condemned as "a different gospel" (see 2 Cor. 11:4; Gal. 1:6). It nullifies the grace of God, for if meritorious righteousness can be earned through the sacraments, "then Christ died needlessly" (Gal. 2:21). Any system that mingles works with grace, then, is "a different gospel" (Gal. 1:6), a distorted message that is anathematized (Gal. 1:9), not by a council of medieval bishops, but by the very Word of God that cannot be broken. In fact, it does not overstate the case to say that the Roman Catholic view on justification sets it apart as a wholly different religion than the true Christian faith, for it is antithetical to the simple gospel of grace.
As long as the Roman Catholic Church continues to assert its own authority and bind its people to "another gospel," it is the spiritual duty of all true Christians to oppose Roman Catholic doctrine with biblical truth and to call all Catholics to true salvation. Meanwhile, evangelicals must not capitulate to the pressures for artificial unity. They cannot allow the gospel to be obscured, and they cannot make friends with false religion, lest they become partakers in their evil deeds (2 John 11).

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Adapted from John MacArthur, Reckless Faith: When the Church Loses Its Will to Discern (Wheaton: Crossway Books, 1994). http://www.gty.org/Resources/Articles/A190_Is-Roman-Catholicism-Biblical?q=Roman+Catholicism