Book One of Ovid's Metamorphoses begins with the creation of the world out of formless chaos. After having created the world, the Metamorphoses proceeds with the creation of life, ultimately culminating in the creation of humanity, which is set apart by its possession of conscious thought. In a way, one might even say that the creation of mankind represents not just the culmination of God's efforts to create life, but also the represents a kind of culmination for the entire act of creation of divine creation: consider Ovid's closing lines for this first section of the poem: "earth was metamorphos'd into man."
Throughout this section of the Metamorphoses, Ovid reflects on one of the critical themes of ancient mythology: the imposition of order over chaos. The world begins with formless chaos, and from that chaos God instills order. That's what the act of creation here is ultimately about, and the same theme is reflected in the creation of humanity. Upon creating the world, God creates the various animals to live upon it, each according to its own proper place (birds are juxtaposed with air, "herds of beasts" with fields, and fish with "oozy beds"). However, order implies rationality, and hence it requires the creation of a rational creature "to rule the rest," as Ovid says. Thus humanity is exalted above all other creatures.