The Ramchal says each one of these events which Klal Yisrael commemorates is not an historical event, rather a certain tikun that was established in the world at that time. These events reflect certain tikunim or certain levels which Klal Yisrael reached at that point in time when there was a certain abundance that came down to creation as a result of that tikun. When we keep these holidays today, we're attempting to recapture the abundance of that tikun that existed then for today and by doing that to activate a similar tikun in creation now. Normally it would be impossible, but when G-d gave us the mitzvos of the holidays He allowed this abundance that once existed to revisit the world every year.