Every great story has to begin with setting the picture.
The Torah boldly departs from the traditional start of the narrative, which usually introduces to us the main protagonist, like in the Epic of Gilgamesh, “Read out the travails of Gilgamesh, all that he went through!” The protagonist then proceeds on the journey of self-discovery, which demands from him (or, in the modern epic, from her) an array of various actions bringing him to the desired result.
Later on, the Torah incorporates the heroic narratives of patriarchs and matriarchs and, after that, the epic story of Moses. However, the start of the Torah narrative establishes the firm fact of God’s existence and the active role of God in creating and shaping the world.
The commentators, debating the choice of the first verse for the Torah, quote Rabbi Yitzchak, who said, “The Torah, which is the book of laws, should have begun with the verse, This month shall be unto you the first of the months,(Exodus 12:2) which is the first commandment given to Israel. What then is the reason that it begins with the creation?”
Because it makes a far more thrilling story, that’s why.