By Clement Harrold

July 30, 2026

Catholics and Protestants disagree on how many books belong in the Old Testament.  

This disagreement is important because the seven books that Protestants reject—often referred to as the deuterocanonical books—contain a number of doctrines that disprove core tenets of Protestant theology.

Here are the three most important examples.  

Intercession of the Saints

The Catholic understanding of the intercession of the saints flows directly from the reality of the communion of the saints (see Heb 12:1).  

We are all united in Christ, and since we are instructed to pray for one another here on earth, it makes no sense to say that this intercession suddenly ceases at the moment of our death. On the contrary, we would expect the souls in heaven to be even greater intercessors than the souls here on earth.  

Several deuterocanonical passages point to the intercession of both the saints and the holy angels:

• And so, when you and your daughter-in-law Sarah prayed, I brought a reminder of your prayer before the Holy One; and when you buried the dead, I was likewise present with you. (Tobit 12:12)
• I am Raphael, one of the seven holy angels who present the prayers of the saints and enter into the presence of the glory of the Holy One. (Tobit 12:15)
• O Lord Almighty, God of Israel, hear now the prayer of the dead of Israel and of the sons of those who sinned before thee, who did not heed the voice of the Lord their God, so that calamities have clung to us. (Baruch 3:4)
• Oni′as, who had been high priest, a noble and good man, of modest bearing and gentle manner, one who spoke fittingly and had been trained from childhood in all that belongs to excellence, was praying with outstretched hands for the whole body of the Jews. Then likewise a man appeared, distinguished by his gray hair and dignity, and of marvelous majesty and authority. And Oni′as spoke, saying, “This is a man who loves the brethren and prays much for the people and the holy city, Jeremiah, the prophet of God.” Jeremiah stretched out his right hand and gave to Judas a golden sword, and as he gave it he addressed him thus: “Take this holy sword, a gift from God, with which you will strike down your adversaries.” (2 Macc 15:12–16)

The first two examples from the book of Tobit reveal how the holy angels are constantly interceding on our behalf.  

The verse from Baruch explicitly implores God to hear the prayers of those who have already died.  

In the passage from 2 Maccabees, the high priest Oni’as intercedes on behalf of the people, and his prayer is answered in the form of a vision of the prophet Jeremiah. What makes the vision significant is the fact that this prophet, who had died hundreds of years earlier, is depicted as one who continues to pray for the Jewish nation and for the holy city.

As early as the third century, the great Scriptural commentator Origen appealed to this passage as evidence that the saints in heaven continue to aid us by their prayers.

It’s worth adding that the intercession of the saints isn’t just found in the deuterocanonical books.  

In Revelation 5:8, for example, the twenty-four elders fall down before God “with golden bowls full of incense, which are the prayers of the saints.” This is significant because in Revelation the elders are representatives of the souls in heaven, while “the saints” who are mentioned in this verse are almost certainly the Christians who are still on earth.

For a more detailed treatment of these issues, see here.

Atonement Through Good Works

Most Protestants adopt a view of the atonement which says that Christ’s saving work on the cross was so all-encompassing that all we need to do to be saved is to respond to Him with an act of faith.  

Catholics, by contrast, take seriously St. Paul’s instruction to “work out your own salvation with fear and trembling” (Phil 2:12).

Salvation must be worked out because Christ’s atoning sacrifice isn’t simply a one-and-done event that we assent to at a particular moment with the result that we’re guaranteed a place in heaven no matter how we live our lives.  

On the contrary, Scripture makes it abundantly clear that we can still lose our salvation if we choose to turn away from God after our initial conversion (see, e.g., Ez 33:12–13).

It’s therefore essential that we learn to participate in Christ’s atonement.  

We must do this throughout our lives as Christians, and our participation takes the form of prayer, suffering, and works of mercy, as the deuterocanonical books affirm:

• For charity delivers from death and keeps you from entering the darkness; and for all who practice it charity is an excellent offering in the presence of the Most High. (Tobit 4:10–11)
• For almsgiving delivers from death, and it will purge away every sin. Those who perform deeds of charity and of righteousness will have fulness of life (Tobit 12:9)
• Water extinguishes a blazing fire: so almsgiving atones for sin. (Sirach 3:30)

The truth of these verses is corroborated at various points in the New Testament.

In the Gospel of Luke, Jesus declares, “But give for alms those things which are within; and behold, everything is clean for you” (Luke 11:41). St. Peter reminds his readers that “love covers a multitude of sins” (1 Pet 4:8). St. James asks: “What does it profit, my brethren, if a man says he has faith but has not works? Can his faith save him?” (Jas 2:14). And in Luke 16:9, Christ solemnly warns His followers to “make friends for yourselves by means of unrighteous mammon, so that when it fails they may receive you into the eternal habitations.”

Purgatory  

The most well-known “Catholic passage” in the deuterocanonical books comes from 2 Maccabees:

On the next day, as by that time it had become necessary, Judas and his men went to take up the bodies of the fallen and to bring them back to lie with their kinsmen in the sepulchres of their fathers. Then under the tunic of every one of the dead they found sacred tokens of the idols of Jam′nia, which the law forbids the Jews to wear. And it became clear to all that this was why these men had fallen. So they all blessed the ways of the Lord, the righteous Judge, who reveals the things that are hidden; and they turned to prayer, beseeching that the sin which had been committed might be wholly blotted out. And the noble Judas exhorted the people to keep themselves free from sin, for they had seen with their own eyes what had happened because of the sin of those who had fallen. He also took up a collection, man by man, to the amount of two thousand drachmas of silver, and sent it to Jerusalem to provide for a sin offering. In doing this he acted very well and honorably, taking account of the resurrection. For if he were not expecting that those who had fallen would rise again, it would have been superfluous and foolish to pray for the dead. But if he was looking to the splendid reward that is laid up for those who fall asleep in godliness, it was a holy and pious thought. Therefore he made atonement for the dead, that they might be delivered from their sin. (2 Maccabees 12:39–45)

This scene provides compelling evidence that intercession for the dead was part and parcel of ancient Jewish practice. But intercession for the dead only makes sense if the doctrine of purgatory is true; we pray for the dead so that they may more quickly enter the joys of heaven.  

Incidentally, this passage from 2 Maccabees also seems to assume the Catholic distinction between venial and mortal sin.  

Judas and his men realize that the fallen soldiers were guilty of sin, but they don’t infer from this that the fallen soldiers are automatically damned. Instead, Judas and his men believe there’s still a chance for the fallen soldiers to be cleansed from their sins with the help of the prayers of those who are still on earth.  

Admittedly, trying to build a whole theology of purgatory on the basis of this one passage would not be very convincing. Thankfully, however, there are multiple other Scripture passages that also support the Catholic doctrine of purgatory (see here for some examples).  

One intriguing passage that isn’t often discussed is 2 Timothy 1:16–18.

Here St. Paul asks the Lord to grant mercy to a certain Onesiph’orus at the final judgment. This is significant because the context of the passage implies that Onesiph’orus has already died (cf. 2 Tim 4:19), which suggests that Paul is offering a prayer for the dead.  

So Which Bible Is Correct?  

It has been cleverly said that one man’s modus ponens is another man’s modus tollens.  

Modus ponens is a syllogism that works by affirming the antecedent (P):

Premise 1 (Conditional): If P, then Q.

Premise 2 (Affirmation): P is true.

Conclusion: Therefore, Q is true.

Modus tollens is a syllogism that works by denying the consequent (Q):

Premise 1 (Conditional): If P, then Q.

Premise 2 (Denial): Q is false (Not Q).

Conclusion: Therefore, P is false (Not P).

Now consider these two forms of argument in relation to the “Catholic passages” from the deuterocanonical books that we’ve been discussing in this blog post.

For the Catholic, it’s easy enough to construct the following modus ponens:

Premise 1: If the Catholic passages are in the Bible, then the Catholic passages are true.  

Premise 2: The Catholic passages are in the Bible.  

Conclusion: Therefore, the Catholic passages are true.  

That’s all well and good, but of course the Protestant will offer a modus tollens that offers a decidedly different perspective:

Premise 1: If the Catholic passages are in the Bible, then the Catholic passages are true.

Premise 2: The Catholic passages are not true.  

Conclusion: Therefore, the Catholic passages are not in the Bible.

It seems, then, that Catholics and Protestants find themselves at an impasse.

And yet, this is precisely where the Achilles heel of Protestant theology begins to bite.

In order to maintain his theological framework, the Protestant has to insist that the Catholic passages are false and that the deuterocanonical books are not part of the Bible.

But this raises an obvious question: How can the Protestant be sure that he’s right about these things? How can the Protestant be sure that he is right and that a figure like St. Augustine (who embraced the deuterocanonical books) is wrong? How can the Protestant be sure that he is right and that all the world’s Catholics and Orthodox are mistaken?  

The inescapable answer to these questions is: the Protestant can’t be sure.

He can’t be sure that the Catholic passages are false, especially when we consider that the passages in question are also supported in other parts of Scripture. Nor can he be sure that the deuterocanonical books don’t belong in the Bible.

But this makes things very awkward for the Protestant.  

The three Catholic doctrines we’ve discussed in this blog post—intercession of the saints, atonement through good works, and purgatory—are really important. These are not peripheral issues.  

Given this, are we really to believe that God didn’t leave us with any reliable means for figuring out which books are part of the Bible?

Did God really make the Bible’s table of contents a matter of guesswork, where Protestants happened to guess correctly, but the majority of the world’s Christians guessed incorrectly?

The Protestant has no choice but to answer these questions in the affirmative.

As Catholics, however, we can avoid all these difficulties because of our superior ecclesiology. Instead of leaving us to guess which books are inspired by the Holy Spirit, God has given us His Church, “the pillar and bulwark of the truth” (1 Tim 3:15), to provide authoritative teaching on which books belong in the Bible, and thus on which doctrines are true.  

Further reading:

5 Bible Passages Which Point to Purgatory

How Can Mary Listen to the Prayers of Millions of People At Once?

Where Does the Bible Talk About Mortal Sin?

Why Are Protestant Bibles Smaller?