According to Donald Parry, "staircase parallelism" is a (Hebrew) poetical device where there is an apparent stepping up from one sense to another, until at the pinnacle is a culmination of thought.
A characteristic often found in staircase poetry is the idea of an ascension from specific to general things. 2 Nephi 29:12 is illustrative of this. Note how the writer first mentions the Jews, one of the twelve tribes. This is followed by mention of two more tribes, Ephraim and Manasseh, which the Book of Mormon calls "Nephites." Then is mentioned the "other tribes of the house of Israel," and finally "all nations."
For behold, I shall speak unto the Jews and they shall write it;
and I shall also speak unto the Nephites and they shall write it;
and I shall also speak unto the other tribes of the house of Israel, which I have led away, and they shall write it;
and I shall also speak unto all nations of the earth and they shall write it
[Donald W. Parry, The Book of Mormon Text Reformatted according to Parallelistic Patterns, F.A.R.M.S., pp. xxi-xxiii]