Prophecy is about God telling us things in advance. That is what prophecy is in the most basic definition possible. But this answer honestly stirs up as many questions as it answers. Why does God go to the trouble to tell us what is going to happen in the future? What is He after in doing this . . . is He just showing off His foreknowledge and omniscience?
Prophecy has a major function according to what is written in Scripture. God is actually doing something here - and He is doing it for a very specific reason. Listen to these words from Isaiah 46,
8 "Remember this, and be assured; Recall it to mind, you transgressors. 9 "Remember the former things long past, For I am God, and there is no other; I am God, and there is no one like Me, Declaring the end from the beginning, And from ancient times things which have not been done, Saying, 'My purpose will be established, And I will accomplish all My good pleasure'; (Isaiah 46:8-10, NASB)
God tells us here that He is giving us prophecies of the future to prove to us that He is God. No one can give an exact representation of the future without error - unless He is a being who sees the future - or as we grasp with God's eternity - He dwells in the future, past, and present all at once. God gives prophecy to prove to us that He is God. That is one of the most important reasons for prophecy. It is also one of the reasons we need to take great care in dealing with it. Too many make prophecy look cheap and tawdry by making prediction after prediction as to who is the antichrist - as well as hundreds of other ignorant guesses as to what prophecy is telling us. The first - and in many ways most important - purpose for prophecy is to watch as God predicts with perfect accuracy - the events that are going to take place in history. God's accuracy at doing this is beyond stunning - it is perfect.
A second reason God gives prophecy to us is for our instruction concerning judgment and correction for His people. We read in Amos 3:7, "Surely the Lord God does nothing unless He reveals His secret counsel to His servants the prophets." Here we see that God announces ahead of time what He is about to do - and does it through His prophets. In the vast majority of cases this involved judgment upon His people. They needed to know that their disobedience and rebellion against His Word was going to bring consequences. Since they were already disregarding His commandments and ordinances - they needed to see and hear something that would remind them He is God. Thus God offered His judgments to them in advance - letting them know what was going to happen. When it did happen - they would be reminded that He is God - and that their rebellion was a serious matter.
The last reason I want to lay before you for prophecy - is that God has chosen to reveal to us what will happen prior to the return of His Son, the Lord Jesus Christ. This God has laid out for us in Scripture. Jesus Christ will come back to this earth just as God says He will. We are watching these things unfold right before our very eyes. We've been watching them for years - and it seems that events are speeding up in our day. Regardless whether Jesus comes back in our generation or not He is coming - and Scripture tells us - He is coming to judge the earth. There is something for which we need to be prepared.
Therefore, be careful about those who want to make prophecy into a "who's the antichrist" guessing contest. As we look at the unfolding of God's perfect history - know this. God is moving this world toward two inevitable events. The judgment of mankind - and the summing up of all things in Christ. Ultimately, this is what prophecy should point us toward. Therefore, rather than having our prophecy site be a "prediction center" for the latest fad in the religiously ridiculous, we're going to try to stick to these things - and to how present history seems to be matching up to the history God told us is going to happen.