This selection is Adam speaking to the angel Raphael, but he is recounting his creation and quoting what God has told him. From the text, it seems that God was literally talking directly to Adam, and not through an emissary as we see in the current events of the story. For example, when Adam and Eve are expelled from the garden, Michael comes as a messenger, rather than God himself bringing the news. Therefore, the "I" in this case is God, and "thee" is Adam. Also worth noting is that this retelling of a story by a main character is a common element in epic poetry.