Why was/is so much veracity given to the Old Testament prophets?
We base a lot of the reasonableness to believe things in the New Testament, like the coming of the Messiah, the life and purpose of the Virgin Mary, etc. on statements found in the prophecies of various Old Testament prophets. What exactly gave those prophets their authority, their believably? What were their credentials? Why did the people of that era, and today, so readily accept their ideas? Why today do we so often try to correlate their prophecies with later events found in the bible?
Today, we laugh at people who claim to predict the end of the world, the second coming of Christ and so on. How did these prophets differ from people today like the late Harold Camping and all his false prophecies?