Can a Roman Catholic be truly Christian given all the false teaching that Catholicism holds?
First, we must separate the institution from those who congregate within it. While we cannot judge a person's heart, we can investigate the teachings and beliefs of a religious system like Catholicism to evaluate whether it accurately reflects the truth of scripture.
In evaluating Catholicism, we find the doctrines, beliefs and practices of the Roman Catholic Church to be unbiblical. By far the most important distinction between Catholicism and Christianity is their teaching on salvation. How one gets to Heaven is the most important question a person can ask, but the answers offered by scripture and by the Catholic Church are radically different, and any religion that does not agree with Scripture regarding salvation is, by definition, a false religion.
Scripture is very clear how one receives salvation. The Bible says that salvation is found by faith alone in Christ alone:
Faith alone in Jesus Christ alone is the means to salvation according to the Bible. Diving deeper, the Bible says that all men are sinners, deserving of God’s wrath. Our sin has separated us from God, and our sin must be punished because God is a holy and just God. To avoid that penalty and enter into Heaven, we must be perfectly righteous and without sin and thus reconciled to God.
So by faith in Jesus our sins have been justly punished (on Christ) and we have been made perfect (by receiving Christ's righteousness), and these outcomes are the result of Christ's work on our behalf, not because of anything we did for ourselves. In fact, the only thing we bring to our salvation is our sin, which Christ takes from us. Any supposed "good" works we might do count for nothing to God since Jesus has accomplished everything necessary for our salvation. That is why we call this truth the “gospel," which means “good news.”
The Catholic church does not hold to this gospel. Although the Catholic Church teaches that a person's salvation begins with faith in Jesus as Messiah, they depart from the Gospel in claiming that faith alone will not secure salvation. Catholics believe they must become perfect before they may enter into Heaven, and they teach the way to perfection is by doing penance for sin and accomplishing righteous works. It's important to note that Catholicism doesn't hold that a believer is assigned the perfection earned by Christ (as the Bible teaches); instead Catholics believe that each believer must become perfect in himself by his own works. This teaching is contrary to the Bible and is a false gospel.
In summary, Catholics teach that salvation is dependent on personal works of righteousness, which stands in stark contrast to Paul's words in Ephesians 2:8-9:
So while we could list many differences between the Catholic Church and biblical Christianity, the most important difference centers on the Gospel itself, and this disagreement over the true Gospel was largely responsible for the rise of the Reformation and the existence of Protestant churches today. In the sixteenth century, the Lord led Martin Luther to shine forth the light of the true gospel again in opposition to the heresy of the Catholic Church by teaching that a person is saved by faith alone in Christ alone. Naturally, Luther's teaching put him at odds with the Catholic Church and the Reformation followed.
At the time of the Reformation, the Catholic church convened a church council to refute the teachings of the Reformers (i.e., Martin Luther, John Calvin, and many others). This council, called the Council of Trent, became the official teaching of the Catholic church and remains their official teaching to this day.
It’s important to note that the Catholic church teaches that when the pope and the magisterium (the bishops of the church) teach something with respect to faith and morals, such as was taught at the Council of Trent, that teaching is infallible. Since it is “infallible”, every Catholic must accept this teaching without question. To do otherwise makes one a bad Catholic, meaning that person would be in open rebellion to the church’s official, infallible teaching. As far as the Catholic church is concerned, it is just as bad as rejecting the Bible.
Examples of this teaching from the Council of Trent are shown below. Remember, each one of these statements is considered infallible and, therefore, equal with Scripture for Catholics, as the Catholic church believes the Holy Spirit leads the pope to proclaim such infallible statements:
These statements all state that anyone who says salvation is by faith alone is categorically wrong and must be excluded from the Church. For the Catholic, salvation is about works, not faith alone.
Clearly, these beliefs contradict Scripture in many places, including:
Romans 5:19, “19 For as through the one man’s disobedience the many were made sinners, even so through the obedience of the One the many will be made righteous.”
Romans 5 provides a contrast between Adam and Jesus. In Adam, we are all made sinners because of his sin. In Christ, believers are made righteous by Christ’s obedience. Notice that it is not by our works that we are considered righteous, as the Catholic church falsely teaches. Rather, it is solely by Christ’s obedience that we are made righteous.
Preaching a different gospel is the most serious error of the Catholic religion (and there are many others), but this difference alone makes the Catholic Church a false religion, as scripture says in Galatians 1:
Though Catholics acknowledge Jesus (then again, even the Muslims acknowledge Jesus), nevertheless the Catholic church preaches a gospel contrary to the one Jesus delivered to us. Therefore according to Paul, the Catholic Church is not a Christian church; it is a false church.
So can we expect believers to be found in the Catholic Church?
Since the Catholic Church presents a false gospel that cannot bring men and women into Heaven and rescue them from Hell, why would a true believer choose to remain in a church that teaches a false gospel? This would be no different than a believer attending a Mormon church, a Jehovah Witness church, or any other false church. Why would a believer stay in a church that teaches and believes that which is contrary to the very word of God?
Nevertheless, some believers (very few in our experience) do choose to remain in the Catholic Church. Some remain because they do not realize the differences between the true Gospel and the teaching of the Catholic Church. Others remain because family ties and tradition overrule sound judgment. Still others remain as a mission to reach other Catholics with the truth. Therefore, we cannot say that there are no believers in the Catholic Church, but where believers can be found in that religion, it is only because God's grace has overcome the false teaching in that system.
Still, choosing to remain in the Catholic system of religion after coming to a saving faith in Jesus Christ may have a negative effect on a person's spiritual development. False teaching impacts a believer’s spiritual maturity and relationships with family and friends. Jesus understood this, too, when He warned in Luke 12:
Christ must come first, even above our family and friends. In Luke 14, Jesus says, “26 If anyone comes to Me, and does not hate his own father and mother and wife and children and brothers and sisters, yes, and even his own life, he cannot be My disciple.” This does not mean we should hate our family; rather, it means we must love Him more than even our family. Therefore, Christians must share the true gospel with Catholics, as this is a truly loving action.