In the phrase in Kaddish "Yitbarach Ve'yishtabah Ve'yitpa'ar…" the word "Ve'yishtabah" begins a series of seven words that consist of six letters each, for a total of 42 letters. This phrase thus alludes to the special "Shem Mem-Bet" – the 42-letter Name of G-d, which has special significance.
If we add the other three words of praise in Kaddish – "Yitgadal," "Ve'yitkadash," and "Yitbarach," we arrive at a total of ten expressions of praise, which parallel the ten utterances with which Hashem created the universe. These ten pronouncements later found expression in the declaration of the Ten Commandments at Mount Sinai. The people heard the first two commandments from G-d, whereas the other eight were told only to Moshe who then conveyed them to the people. Accordingly, the ten expressions of praise in Kaddish are separated into two series: the two expressions of "Yitgadal" and "Ve'yitkadash" at the beginning of Kaddish, and the eight expressions from "Yitbarach" through "Ve'yit'halal," which appear later.
The Peri Hadash (Rav Hizkiya Da Silva, 1659-1698) writes that these ten expressions of praise correspond to the ten different terms that King David used in Tehillim when praising Hashem (e.g. Nisu'ah, Niggun, Shir, Mizmor).