"the everlasting watchfulness, which Homer hath ascribed to Jove himself"

In ancient Roman myth and religion, Jupiter, or Jove, is the king of the gods, and the god of sky and thunder.  His vigilant watch makes him guardian of public oaths and the guarantor of good faith. 

In Homer’s The Iliad, 800 B.C, Book XX tells of the stirrings of war between the Achaeans and the Trojans:

“Meanwhile Jove from the top of many-delled Olympus, bade Themis gather the gods in council, whereon she went about and called them to the house of Jove… When they reached the house of cloud-compelling Jove, they took their seats in the arcades of polished marble which Vulcan with his consummate skill had made for father Jove...   

Neptune also, lord of the earthquake, obeyed the call of the goddess, and came up out of the sea to join them. There, sitting in the midst of them, he asked what Jove's purpose might be. "Why," said he, "wielder of the lightning, have you called the gods in council? Are you considering some matter that concerns the Trojans and Achaeans- for the blaze of battle is on the point of being kindled between them?"And Jove answered, "You know my purpose, shaker of earth, and wherefore I have called you hither. I take thought for them even in their destruction. For my own part I shall stay here seated on Mt. Olympus and look on in peace, but do you others go about among Trojans and Achaeans, and help either side as you may be severally disposed… Thus spoke Jove and gave the word for war, whereon the gods took their several sides and went into battle.”