Parallel grammatical construction form means that each part of a sentence uses the same grammatical structure. It is also known as a balanced structure within one or more sentences of similar phrases or clauses having the same grammatical structure.
These are the Different kinds of parallel structures that we can make:
Synonymous parallel structures occur when the different constructing clauses of a sentence have a similar meaning.
Antithetical parallel structures occur when the different constructing clauses of a sentence have an opposite meaning.
Climatic parallel structures occur when a part of a clause ir repeated in subsequent clauses within the sentence.
Emblematic parallelism is etymologically derived from the word emblem, which means "symbol." Parallelism occurs in poetry when lines are intentionally placed together to create comparison, contrast, or enhancement of a meaning.
Synthetic parallelism involves the completion or expansion of the idea of the first part in the second part.
The type of Parallel structure used here is:
Synthetic parallelism
for the Psalm here starts by saying the Lord is good, then expands that same idea by saying that his mercy is everlasting.