Fulfilled Biblical prophecy is often cited at atheists as proof that a God exists, but we are not buying it. Why not?

First, there's a logical disconnect. Suppose it were true that the Bible did accurately forecast future events. How does that demonstrate a god? Why not time travelers, aliens, or the simple ability of a person to see into the future, as a magical power? From our perspective, the theist has simply chosen the preferred conclusion out of many possibilities.

Often, the connection between fulfilled prophecy, and God, is just a fallacy of association. A book makes Claim X (prophecy), which turns out to be true. The book also makes Claim Y (God exists), and because it is in the same book as Claim X, it must also be true.

That is not how demonstration works. It would be fascinating if a 2000 year old book reliably, accurately and specifically predicted the future, but if you claim that this was due to a god, you have to actually demonstrate that mechanism. Otherwise, all we know is that people 2000 years ago somehow had knowledge about the future.

Beyond that, we can examine the nature of "prophetic claims", to evaluate whether they indicate there's anything to them.

Do you buy into horoscopes? If one is interested in knowing whether they "work" or not, we can find ways of evaluating them. For instance, one can go through the description for each sign, and rank each assertion as to how well they match your life and personality. Tally up the sums for each sign, and compare them to each other. You'l likely find that the majority of the signs match you fairly well, and many may match you better than the description for your own astrological sign.

That is the point when you might realize that it is essentially an inkblot test, where you're reading vague, broad statements, and matching them to your life... and that is it. Once you realize that, it is easy to understand that it is bunk, and is no longer compelling or interesting.

Analyzing Prophecy

For the sake of argument, let's grant that Biblical prophecy at least appears to come true. Similar to analyzing astrology, we can find a way to analyze this too. We can ask a question, "Can prophecy appear to come true without any magic of supernatural beings needed?" The answer is yes. Below is a quick list of a number of different ways this can happen.

Broad, vague claims

Like the horoscope, if the claims are broad or vague enough, we can fit them to any number of events. If I were to predict, "At the beginning of the third millennium, a nation will fall", is that compelling?

You already know that nations rise and fall frequently, so we are not exactly going out on a limb.

Time-Unbounded

Unlike my prediction, the Bible does not often actually give any expiration date. When it does, it usually gets it wrong. For example, Matthew 16: 27, 28 says[1]:
27 For the Son of Man is going to come in his Fathe's glory with his angels, and then he will reward each person according to what they have done.
28 "Truly I tell you, some who are standing here will not taste death before they see the Son of Man coming in his kingdom."
So apparently, the 2nd coming already came and went. The world is a dynamic and active place, and if there's no set time and place, it is just a matter of time before something seems to fit the bill. If I predict that "The leader of one nation will punch another in the face", it may take 5000 years, but it'll eventually happen (assuming humanity does not perish in the meantime).

Fitting the facts to fit the prediction

Suppose a prediction said that "a violent nation will rise and cause destruction." That might be ISIS/ISIL, but is it a "nation"? The moment you say, "well, that is close enough", you're changing/fitting the facts to meet the prediction. Combined with vague predictions, this makes it extremely easy for predictions to appear to come true.

The Christian assessment that we are in the "end times" stretches back to the formation of the Bible. That is because they are in a continual process of looking at current events, and fitting them into Revelations predictions. They've been doing this for hundreds, to thousands, of years.

Going back to my "at the beginning of the third millennium, a nation will fall" example, what constitutes "at the beginning"? One day? A month? A year? 50 years? Are you saying that in a 50-year stretch, no nations will fall?

If a prediction makes Claim A, and you're willing to accept events B, C, D, E, F, G, H, I or J as potentially fulfilling it, doing so does not require magic.

The book proving the book

Mysteriously, atheists will get arguments that the events of the New Testament fulfill the prophecy of the Old Testament. That is not exactly surprising to us. We often characterize the New Testament as "fan fiction", expanding on the old. From our perspective, what they are saying is that the Bible makes a prediction... and then the Bible says the prediction came true. That is not interesting.

It is also notable that the Jewish don't think Jesus actually fulfilled messianic prophecy from the Torah/Old Testament[2].

Self-fulfilling Prophecy

This is more psychological - someone is told that something will come true, and by mere fact of being informed, will (subconsciously or not) make it happen. Telling someone that he/she will be "unhappy next week" (such as in a horoscope), it may act like a placebo effect, and the person will find reasons to be unhappy. Likewise, telling a teenager that he/she will be a famous person may cause that person to work towards the goal, ultimately accomplishing it. Another example is ordering a steak at a restaurant, and predicting that you'll get one. Unless a meteor hits the restaurant, that "prophecy" will likely come true.

A primary example of this in the Bible is the formation of Israel. That prediction was in the book, and known by many people, for a long long time. It was only a matter of time before people worked to make it happen. Ironically, it is often presented as the "slam dunk" example of fulfilled prophecy, but is actually the least compelling.

Predicting Likely Events

Not quite the same as the self-fulfilling prophecy, predicting events, that were likely to happen in the first place, does not take a lot of supernatural sense. If I were to predict that this next summer, the continental U.S. will be hit by a hurricane, does that require divine intervention for me to make that prediction, and it come true? Or am I just extrapolating existing patterns in reality?

Scattershot predictions

Suppose you're at a firing range, and you're blindfolded. You're trying to hit the bulls-eye on a target on the far side of the field. Given enough bullets and time, even firing in random directions, it is just a matter of time before one of those nails it. If we focus on that one that hit, and ignore the rest that missed, it would appear as though the shooter has a 100% accuracy rate.

The Bible says many things.

Educated guesses

It does not take a rocket surgeon, who is living 1800-2000 years ago, to examine the current state of political affairs and figure out patterns. If Christian persecution was already happening at the time, and one understands why, it is reasonable to predict that it might continue in the future. Figuring that out does not require an omnipotent being whispering in your ear.

Very often, part of the argument atheists get, asks, "what, you think they just randomly guessed all this correctly?" It is not a dichotomy between complete guesses and divine knowledge. A third category - educated, evidence-based predictions - can get you a long way towards reasonably predicting the future.

Given today's state of affairs, do you think it is unreasonable to predict that, at some unspecified point in the future, that the U.S.A. is probably going to collapse as a nation? Did you require a universe-creating being to figure that out?

Conclusion

At the end of the day, when we actually examine the cited examples of "fulfilled" prophecy, we find that they are always combinations of one or more of the above. Each item listed can dramatically increase the probability of a prediction "coming true" without any magic involved.

We can ask ourselves, which is more likely, that the predictions are only appearing to come true, as a kind of optical illusion, or that an invisible infallible magical creature told Biblical authors what to write down, but somehow didn't accurately communicate most of the details?

Each time Biblical prophecy (or Quranic scientific "facts", for that matter) is brought up, it is just tedious, but like many topics, the atheist is left explaining epistemology of the topic for the hundredth time. That can be annoying.