By Rabbi Berach Steinfeld
During the Musaf Shemoneh Esrei of Rosh Chodesh we include a special Tefillah for the mizbeach. We say “Mizbeach hachadash b’Tzion tachin.” (A new mizbeach should be prepared in Tzion.)
The question arises; why don’t we daven this tefillah in the Shemoneh Esrei of Mussaf for Shabbos or Yom Tov? Why do we say it only in the tefillah of Rosh Chodesh?
There are a number of answers to this question.
The Rokeach answers that the posuk teaches us “Vehaya midei chodesh bechadsho umidei Shabbos be’Shabbato…“ The posuk is telling us that reshaim are judged again every week on Shabbos. Since Gehinom’s fires are stoked every month, Chazal established a special tefillah for the mizbeach, which counteracts the fire of Gehinom.
Another answer is that in general Rosh Chodesh is a zman kaparah. We therefore daven for the mizbeach which is the source of kapara.
A different response it that since the building of the Bais Hamikdash is not docheh Shabbos or Yom Tov; we therefore do not daven for the new mizbeach on Shabbos or Yom Tov.
The problem with this last answer is that Tosfos in Rosh Hashana, daf lamed and Tosfos in Sukka, daf mem alef say that the binyan hashlishi may come down even on Shabbos and Yom Yov.
We could differentiate that since korbanos for forgiveness were not brought on Shabbos and Yom Tov that is the reason why we only daven for the mizbeach on Rosh Chodesh.
May we merit having the mizbeach in our time so we can properly have a kapara.