There are many significant events in the history of the world.  Great men and leaders have risen and fallen.  Great civilizations have been established and others destroyed.  Great movements and developments and advancements have been made in language and science and knowledge.  But the advent of Christ was the greatest event in all of history to that time, as Jonathan Edwards explains:

Christ’s incarnation was a greater and more wonderful thing than ever had yet come to pass. The creation of the world was a very great thing, but not so great as the incarnation of Christ. It was a great thing for God to make the creature, but not so great as for the Creator himself to become a creature. We have spoken of many great things that were accomplished between the fall of man and the incarnation of Christ: but God becoming man was greater than all. Then the greatest person was born that ever was or ever will be.