Let's break down why:
* Biblical Allusion: The phrase directly references the verse in Psalm 23:5, "Thou preparest a table before me in the presence of mine enemies: thou anointest my head with oil; my cup runneth over." This alludes to the idea of abundance and overflowing blessings, often in the context of God's favor.
* Metaphor: The "cup" represents something beyond its literal meaning. It symbolizes blessings, happiness, or even something like love or joy. "Runeth over" suggests that these blessings are overflowing, exceeding expectations and reaching a point of fullness.
It's important to note that without the context of the poem, we can't be sure what specific meaning Pryor is assigning to the phrase. However, the use of "cup runeth over" strongly suggests a theme of abundance, fulfillment, or exceeding expectations.