The Aruch Hashulchan asks, “Why are we allowed to say the Tefillah
Of Yehi Ratzon (Shabbos Mevorchim)
On Shabbos you may not daven for personal needs. (Chayim Aruchim
He writes , If it were up to him, he would abolish the wholeTefillah.
The reason for saying the Tefillah of Mi Sheoso Nisim, is because
Rosh Chodesh was the first Mitzvah after Geulas Mitzrayim, so
we daven for the Geulah to come again Bimheira V’yomeinu.
This will happen when Chaveirim Kol Yisroel.
The Baer Heiteiv quotes the Sefer Minhagim, to skip the
word Bekarov (Hu Yigal Osonu) so that you will have 21
words in the Tefillah, the Gematria of the Sheim , אהיה
and the Gematria of אך טוב