The importance of this subject in the Bible is underscored by the fact that God declares that the words of Jesus are "the spirit of prophecy" (Revelation 19:10). The apostle Peter reminds us that its importance derives from the fact that it is not the creation of the mind of man but rather something that originates from God himself (2Peter 1:21).
There are many reasons why we should study what the Bible says about this subject. The first reason is that almost two-thirds of Scripture, in one form or another, is related to prophecy. This fact alone warrants our attention! Additionally, the apostle Paul states that the prophetic word, in the Bible, exists for our instruction and benefit (2Timothy 3:16 - 17).
The second and third reason regarding the important of prophecy is that it is a proof of God's existence and that he has the power to do as he wills. The accurate fulfillment of predictions in the Bible, in every detail within a specified time frame, testify that a divine Creator does exist and that he has the power to influence people's lives and foreordain events on planet earth.
God, in the Bible, accurately predicted, and made come to pass, the rise of world empires like Persia and Rome (Daniel 2:32 - 33, 40 - 41, 7:7, 8:3 - 4, 20). He also predicted the rise of the Greek empire through Alexander the Great. Additionally, he foretold that not one of Alexander's family would rule the empire after his death and that it would split into four pieces (Daniel 8:21 - 22).
The accurate prediction of his own death and the exact length of time he would be dead was the only sign Jesus gave religious leaders that he was the Messiah (Matthew 21:38 - 40). He testified of his own divinity during his unjust trial when he foretold what the hateful religious leaders, who wanted him dead, would soon prophetically see (Mark 14:61 - 62).
Bible prophecy testifies to God's plan for man. For example, it predicts at least two resurrections from the dead. The first one shows God has planned a reward to those who believe in him (1Thessalonians 4:16, Revelation 20:6). The second resurrection tells us God will soon offer all humans a full chance at understanding and receiving salvation (Ezekiel 37:1, 5 - 6, 11, see also Revelation 20:5, 13).
Prophecy in the Bible is, many times, our Creator's advance warning that there are very REAL consequences to the choices we make and actions we take in this life. Nobody ultimately "gets away with" sinning. What we do will, eventually, catches up with us (1Timothy 5:24). God used Jonah to warn ancient Nineveh that its sins would soon bring his judgment upon them (Jonah 1:1 - 2, 3:4).
In a rare occurrence that warranted its mention by Jesus (Matthew 12:41), the people of Nineveh heeded the warning of their destruction and repented. Their actions, according to the Bible, changed their fate from death to life (Jonah 3). Prophecy serves many purposes. It helps us not only understand the mind of our Creator but also can teach us valuable lessons.