Because they were written down well before the event happened. One of the greatest prophetic psalms is Psalm 22.... written at least about 1,000 years before Christ. This was the psalm that Christ recited on the cross... it begins "Oh, God, oh God, why have you forsaken me?"
So what do we find in this psalm?
"But I am a worm, and no man; a reproach of men, and despised of the people. All they that see me laugh me to scorn: they shoot out the lip, they shake the head, saying, He trusted on the Lord that he would deliver him: let him deliver him, seeing he delighted in him."
and:
"The assembly of the wicked have enclosed me: they pierced my hands and my feet. I may tell all my bones: they look and stare upon me. They part my garments among them, and cast lots upon my vesture."
There is a prophecy about him in the Bible. All people that reject the Lord Jesus Christ and what He did on the cross for all that would believe and trust in Him will go to hell. He died for our sins was buried and rose again the third day for our justification. Romans 4:25 Who was delivered for our offences, and was raised again for our justification.
You might have a point if one was dealing with word of mouth only. But you have texts that are written with dates can can be reasonably ascertained. Unless you are asserting somebody had a time machine witnessed events and then traveled back in time to write them down (and some evidence to support that assertion), we have written prophecies that predate the events.
there is a very strong argument that nostradamus' prophecies were not in fact predictions of the future, but social commentary on world events of his time under the guise of prophecy so he didn't get beheaded.
basically (outside the social commentary on current times which is not meant to really be a future prediction) any prophecy that lacks specificity Ie: exact event, exact date time and place, etc. so as to remove any real doubt, is a load of crap.
anyone can make a broad, vague blanket statement that idiots will try to fit future facts into to satisfy their sense of mysticism and need for fantasy.
The Dead Sea scrolls were written 300+ years before Jesus was born. The book of Isaiah is included in those scrolls which has many prophecies concerning Jesus... and the scrolls contain many other Old Testament books.
Ever hear of the Bible Code?
They are prophecies that have been in the bible for thousands of years which are
coming to past in this day and age, with well known names and events.
The Wright Brothers, airplane, Hitler, World War 2, Atomic Bomb, John F. Kennedy,
Assassination, Twin Towers, and many others, all that have come to pass. And those
are just a few that come to mind. Now, you can be a fool and say those
are just coincidences or some other lame excuse, but they are true no matter who
accepts them or not. Hating the bible or Christianity won't make them not be true.
Also read 2 Timothy 3:1-13 which also prophecy's of the changes that will come by
mankind that are again happening today. Those of us that grew up in the 1940's and
early 50's can see the differences that are taking place in America today, which were
also prophesied way back when; up to and including the renewed persecution of Christianity.
.
How about Daniel 2 where Nebuchadnezzar had a dream he couldn't remember, and God told Daniel the dream and the interpretation of it ?
Thou, O king, sawest, and behold a great image. This great image, whose brightness was excellent, stood before thee; and the form thereof was terrible. This image's head was of fine gold, his breast and his arms of silver, his belly and his thighs of brass, His legs of iron, his feet part of iron and part of clay. Thou sawest till that a stone was cut out without hands, which smote the image upon his feet that were of iron and clay, and brake them to pieces. [ Dan 2:31-34 ]
This statue was the prophecy of ALL the nations from Babylon to the Second Coming of Jesus, and other than the Second Coming can be verified from history.
The 'head of gold' was Babylon 605 - 538 B C
The 'breast of silver' was Medo-Persia 538 - 331 B C
The 'thighs of brass' was Greece 331 - 168 B C
The 'legs of iron' was Pagan Rome 168 B C - 476 A D
The 'feet of iron and clay' is the divided kingdoms, firstly Papal Rome, then all the nations that exist today.
And 'the rock cut without hands' is the Second Coming of Jesus Christ, your Saviour and mine.
This is Daniels basic prophecy and was added to in the succeeding chapters,
and even foretold Jesus birth, death and also the end of Judaism as the chosen people.