The correct answer is A) to explain how to honor King Ptolemy and his ancestors.
The sentence that best describes the purpose of the excerpt is "to explain how to honor King Ptolemy and his ancestors."
We can clearly see this while reading parts of the excerpt such as "...increase greatly the existing honors of King PTOLEMY, likewise those of his parents, and of his ancestors, and to set up in the most prominent place of every temple..."
Ptolomy was the King of Egypt in 305 BC. This period is known as Ptolemaic Egypt. His dynasty lasted so many years and ended when Cleopatra was killed in 30 BC.