[1] The reigning emperor was Kōkaku Tennō' (光格天皇).
[2] As is customary for choosing nengō, the name was selected from a passage in a historical Chinese text.
In this case, the text was Classic of History (書経) (also quoted in The Great Learning (大學)), more specifically from the first of the King Tai Jia (大甲) chapters.
It says: "先王顧諟天之明命..." meaning "The former king kept his eye continually on the bright requirements of Heaven, [and...]."
This is continued with a description of reverence, virtue, and prosperity for the lands.