The arc of the moral universe is long but it bends toward justice what does that mean?

References to "the arc of the moral universe" is a metaphor for a 360-degree circle that represents all of morality. Thinking in terms of a complete sphere helps us feature morality in terms of our continuous movement forward. With every act of morality, the moral sphere extends further. Many thinkers, beginning with Dr. Martin Luther King, refer to this moral universe as the arc (or partial circle) that bends toward justice. In other words, morality shows a preference toward truth and justice that far exceeds the countervailing arc of immorality and injustice.

I believe if you read the quote in its first published form you will get a more complete answer. The quote is from Theodore Parker in the 1850s.

"I do not pretend to understand the moral universe; the arc is a long one, my eye reaches but little ways; I cannot calculate the curve and complete the figure by the experience of sight; I can divine it by conscience. And from what I see I am sure it bends towards justice."

Dr. King paraphrased the quote and made it more modern and succinct but it lost some meaning.