What is the name of the literary device where successive lines paraphrase each other?

Question

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

1. every valley shall be exalted (Yes),
2. every hill and mountain shall be made low,
3. the rough places will be made plain (Yes),
4. 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.

Answer 1

The device of repeating the same idea in different words is called restatement. It's used to provide emphasis and clarity to the idea being expressed. Franklin Delano Roosevelt's first inaugural address (1933) furnishes an example:

Nature still offers her bounty and human efforts have multiplied it. Plenty is at our doorstep, but a generous use of it languishes in the very sight of the supply. (emphasis added)

Patrick Henry also used restatement extensively in his 1775 "give me liberty or give me death" speech to the second Virginia Convention:

There is no peace. The war is actually begun! The next gale that sweeps from the north will bring to our ears the clash of resounding arms! Our brethren are already in the field!

Each of these sentences restates the idea that war is underway.

The examples you give, however, are not merely restatements. The rhetorical devices in those passages have specific terms associated with them. Repeating the same words at the beginning of a phrase is called anaphora:

may my right hand forget its skill.
May my tongue cling to the roof of my mouth.

Or looking at the same psalm in the Authorized King James Version:

If I forget thee, O Jerusalem,
let my right hand forget her cunning.
If I do not remember thee, let my tongue cleave to the roof of my mouth;
if I prefer not Jerusalem above my chief joy.

The repetition of "If I" at the start of three phrases and "let my" at two is an example of anaphora. The first two conditionals are also an example of parallelism.

Dr King also uses both anaphora and parallelism in the excerpt you have quoted. Additionally, there's another rhetorical device in this set of opposed ideas:

every valley shall be exalted,
every hill and mountain shall be made low

This is an example of antithesis, when a contrast is used for rhetorical effect.

Answer 2

Perhaps Litany. That link gives this definition:

Initially a prayer or supplication used in formal and religious processions, the litany has been more recently adopted as a poetic form that catalogues a series. This form typically includes repetitious phrases or movements, sometimes mimicking call-and-response.

and this as an example:

Equestrian Monuments (A Litany)
BY LUIS CHAVES
TRANSLATED BY JULIA GUEZ AND SAMANTHA ZIGHELBOIM

Out-of-focus photographs in front of equestrian monuments.

The fog of the drug, low-impact anecdotes and scenes from badly dubbed films.

With this we arrive at our 40s and we shouldn’t be ungrateful.

It could be worse.

…

— Equestrian Monuments (A Litany) by Luis Chaves | Poetry Magazine