The literary device I'm thinking of is when you say something, then you say it again using different words, or words which are equivalent in meaning. For example, in Psalm 137
If I forget you, Jerusalem,
may my right hand forget its skill.
May my tongue cling to the roof of my mouth
So, "may my right hand forget its skill," is roughly equivalent to "May my tongue cling to the roof of my mouth".
Or in the MLK speech he says:
I have a dream that one day
- every valley shall be exalted (Yes),
- every hill and mountain shall be made low,
- the rough places will be made plain (Yes),
- and the crooked places will be made straight (Yes), and the glory of the Lord shall be revealed [cheering], and all flesh shall see it together.
Lines 1-4 are more or less equivalent. I looked up all of the literary devices that I was unfamiliar with at https://literarydevices.net/, but then I realized that I was only looking at a list of the popular literary devices, and that the complete list would take too long to browse.