The primary purpose of a prophet is declare God’s impending punishment of a people if the people do not repent and turn back to God.
Isaiah in the Old Testament was a prophet. Read through the Book of Isaiah and see what Isaiah the Prophet said.
As the video above shows, many Christians believe that prophecies of Isaiah keeps repeating itself in human history in cyclic ways (cycles) until the coming of Jesus Christ.
In other words, just as the prophecy of Isaiah against Damascus was fulfilled in the days of Isaiah, the same prophecy is fulfilled in the New Testament era and in the modern era. It keeps being fulfilled.
In the same way, Isaiah’s prophecies against Israel and the Jewish people keeps being fulfilled, again and again, in history, in cyclic way.
That is why Jerusalem was completely destroyed in the Old Testament. That is why Jerusalem was completely destroyed in the New Testament (70 AD). That is why the prophecy of Isaiah will be fulfilled and Jerusalem will be completely destroyed again in the modern times. Prophecies of the Old Testament keeps being fulfilled in cyclic forms.
Most Christians agree that this is true.
Prophecies of the Old Testament will be fulfilled in the modern era as well.
Prophet’s primary role is to declare the impending destruction that God will bring about as a judgment for not following the Word of God, generally as nations.
When Israel went away from the Word of God as a nation (not only as individuals!), God sent prophets to judge the nation as a whole, based on the direction of the leadership / national laws that went against God’s Law.
Laws of nations / policies of the politicians is the reason why God sends prophets against nations to declare God’s impending justice against that nation.
Just read the prophecies of Isaiah and Jeremiah.
Judgment is of nations for nation’s policies and laws that go against God’s Word.
Prophet’s primary role is the last warning in God’s justice system, before God actually carries out God’s declared punishment.
It is the very last chance to repent and be right with God as a nation, before God fulfills His promise (declared, impending justice of God).