What is the Common Denominator of Jewish History?

When we read the different introductions that the sages gave to the Megilas Esther, we should understand that there is a common denominator with all of them.  Which is the common denominator of everything that happens in history?  It is the common denominator of all the phenomena that we see in nature: Hashem is G-d. — Preface to Purim 2 (#112)