To many non-Catholics, the Crusades were a violent attempt by popes and European monarchs to destroy peaceful, flourishing Muslim kingdoms in the Middle East and reestablish the reign of Christianity. Many Catholics also buy into this narrative, blushing whenever the Crusades are brought up in conversation.

On the other hand, some Catholics see the Crusades as fully justified attempts to defend Christianity in the Holy Land against invading Muslim armies.

Both versions contain some elements of truth. The Crusades are too complex to be considered fully good or bad. There were Crusaders who were driven by just and unjust motives and each Crusade was different, so they all must be evaluated on their own merits.

Let’s begin with this: Many modern narratives of these expeditions leave out or belittle the reality of Islamic aggression in the early Middle Ages. Since the death of Mohammed in the 7th century, Islam spread rapidly by the sword. Palestine, North Africa, Syria, and many other formerly Christian and Jewish lands quickly fell to the new regime of the Prophet.

Also, while there were periods when conquering Muslim leaders exercised tolerance toward their Jewish and Christian subjects, there were also many periods of persecution. Christians were sometimes enslaved, raped, or subject to higher taxes than their Muslim neighbors. They were pressured to convert to Islam and killed if they refused.

Protestants believe in sola scriptura, which means the Bible is the ultimate authority for the Christian life. Catholics believe that Scripture and Sacred Tradition are both authorities, and the authoritative magisterium provides binding interpretations of them.

Here’s why Catholics can’t embrace sola scriptura.

The Bible itself rejects the idea.
Nowhere in Scripture does it claim to be the sole authority for the Christian life. Jesus doesn’t tell His apostles to write Gospels; rather, He commissions them to preach the Gospel.

If you claim that sola scriptura is true but can’t find it in the Bible, you’re appealing to another authority outside of Scripture.

The Bible offers Sacred Tradition as an authoritative guide.
In 2 Thessalonians 2:15, St. Paul says, “So then, brethren, stand firm and hold to the traditions which you were taught by us, either by word of mouth or by letter.”

“By mouth or letter” sounds a lot like Scripture and Sacred Tradition!

In Matthew 16:18–19, Jesus tells Peter, “You are Peter, and on this rock I will build my church, and the powers of death shall not prevail against it. I will give you the keys of the kingdom of heaven, and whatever you bind on earth shall be bound in heaven, and whatever you loose on earth shall be loosed in heaven.”

Catholics have traditionally pointed to this passage as evidence that Peter was given authority over the other apostles and the Church — an authority passed on to his successors, the popes.

However, in Matthew 18:18, Jesus tells all of the apostles, “Truly, I say to you, whatever you bind on earth shall be bound in heaven, and whatever you loose on earth shall be loosed in heaven.”

Does this prove that Peter actually has no special authority?

Not quite. But before explaining why, let’s look at the meaning behind the keys and the terms “binding” and “loosing.”

The Old Testament backdrop to Matthew 16 and 18