The Bible says that God made man in his own image and likeness. At a primitive level, this means that human beings “look like” God. However, God is not a physical being, so it means that the human souls created by God have a nature similar to his (but not as perfect). The author says that whether or not what the Bible says is true (that God made human beings to be similar to Him), it is clear that when human beings make up gods, the ones they imagine are similar to humans.
“His” is spelled with a capital letter, because it’s traditional in English and other European languages to begin all pronouns referring to God with capital letters, so you get He, His, You, etc.
“Ritual is more fundamental than mythology” means that people perform religious and other rituals long after they may have stopped believing in the ideas (or sometimes myths) that underlie the rituals. Many atheists celebrate Christmas, for example. You can find the word “magic” in a dictionary. “Traditional rites” are traditional rituals. “Promotion of fertility” means encouraging people to have children. “Survivals” here means ideas and practices that remain (survive) after a society’s beliefs have changed.
The first paragraph says that if you look at the stories about the Greek gods and their behavior, you can learn a lot about the Greeks who thought up these stories and imagined these gods.
The second paragraph talks about old magic and myths that survived from very ancient times. It says that the Greek religion and mythology developed on their basis, but that so did the beginnings of modern science.