Irenaeus' emphasis on the unity of God is reflected in his corresponding emphasis on the unity of salvation history. Irenaeus repeatedly insists that God began the world and has been overseeing it ever since this creative act; everything that has happened is part of his plan for humanity. The essence of this plan is a process of maturation: Irenaeus believes that humanity was created immature, and God intended his creatures to take a long time to grow into or assume the divine likeness.