No one seems to have mentioned the obvious, so allow me.
First epistles written by Paul: c. 50 AD
Gospel of Mark: c. 60 AD
Gospels of Matthew & Luke: c. 70-80 AD
Gospels of John: c. 90 AD
(this is rough, and I don’t want to quibble over a year or two. It doesn’t matter.)
Foundation of Catholic Church? At Pentecost–33 AD (and yes, we could quibble over that, too–was is really 30 AD, 31, etc. It doesn’t matter.)
The point is that the Church was in existence for roughly 17 years before the first epistle appeared. It was in existence for roughly 27 years before the first Gospel appeared.
So if you assume, as our Protestant friend does, that Scripture is the highest authority, you have to explain how the Church operated for at least 17 years before ANY scripture was available. The answer of course is oral tradition and consensus of the community (a good Islamic concept as well.)
The next step is to ask WHICH scriptures were accepted as authentic by the Church. Luckily, the Gospels the Church does not accept (Thomas, Judas, etc.) were all written later than John. What if a writing of Mark was altered (for example, the end of Mark is generally acknowledged to be an addition to the original)? Well, if the Church accepted it, that made it official. It was part of Scripture. So the Church validates Scripture, not the other way around.
The next step, esp. if you are explaining things to a Muslim, is to explain that Scripture holds the exact opposite position it holds in Islam. In Islam, you are dealing with an uncreated Qur’an (except if you are a Mu’tazila, etc.) which was gradually revealed to Muhammad over a period of time–20-25 years. So Muhammad has to justify his actions (fighting during Ramadan, having more than 4 wives, marrying the ex-wife of an adopted son, etc. etc.) by having a revelation to justify those things; a revelation that existed before time, but was revealed to men through Muhammad at a specific time. So for a Muslim, the Qur’an comes before (chronologically) everything, and thus the Qur’an must justify everything a Muslim believes. To a Christian, it’s the opposite: the Church came first, then the Scripture. The Church decided what Scriptures were authentic. The Church decided what the Scriptures meant, not vice versa.
Do the Church and Scripture support each other? Of course. But does that mean that if something is not specifically mentioned in Scripture (infant baptism, for example), it is not allowed? Of course not. Jesus said, “What you bind on earth is bound in Heaven, what you loose on earth is loosed in Heaven.” In other words, Jesus specifically gave the Church the power to make (and change) rules (not doctrines, rules). Now there are some doctrines (for example, the divinity of Jesus) which were only fully understood over time. You can certainly point to passages in Mark, Matthew, and Luke that show Jesus thought of himself as God, as did others (like his Jewish enemies). But you have to wait until John (c. 90 AD) to have an explicit passage like “In the beginning was the Word; and the Word was with God, and the Word WAS God.” Jesus = Word = God. The same idea exists in Islam–doctrines and rules are better understood over time. A classic example is wine–the Qur’an says there is much good in wine; then it says to be moderate in its use; then it forbids its use. A Muslim would explain this as people needing time to understand an idea. Same thing in Christianity.
No one has quoted Dei Verbum from Vatican II, so allow me: “…the books of Scripture must be acknowledged as teaching solidly. faithfully and without error that truth which God wanted put into sacred writings for the sake of salvation.” Let’s leave the Old Testament aside (although you can immediately see that all that stuff about concubines, killing all the men, women, and children of the Amelikites, killing the priests of Baal, etc. has nothing to do with “…that truth which God wanted put into sacred writings for the sake of salvation.” Therefore, although it’s part of revelation, it’s not necessarily inspired, and can be disregarded–which is why we don’t see Christian sects running around saying “in Kings, God told us to kill all the priests of Baal, therefore we should kill all priests of pagan religions.” Doesn’t happen. Never did.)
But let’s look at the Gospels. Muslims love to point out all the discrepancies in the story of the Resurrection as told in the four Gospels. And they’re right–each Gospel has different details about who arrived first, who they met, where Jesus appeared first after the Resurrection, and John even puts the Last Supper and Crucifixion a few days earlier than the others. Does this mean the Gospels are “corrupt” or “untrustworthy”? No, of course not. It means the details don’t matter. What is “that truth which God wanted to put into sacred writings for the sake of salvation”? That Jesus rose–physically–from the dead. All Gospels agree on that. That Jesus showed himself–again, physically–to his disciples. All Gospels agree. The other stuff doesn’t matter. So there are four stories, each slightly different, but all agreeing on the main point of the story–Jesus rose from the dead.
