והיה מדי חדש בחדשו ומדי שבת בשבתו יבוא כל בשר להשתחות לפני אמר ה' (ישעי' סו-כג)
Since Shabbos falls out on Rosh Chodesh, the Haftorah from the "שבעה ד'נחמתא" is suspended and the Haftorah of Shabbos Rosh Chodesh is read instead. In it, Yeshaya HaNavi declares: “It will then come to pass that every Rosh Chodesh and every Shabbos all mankind will come to bow before Me, says Hashem.” But is it possible to say that every single Shabbos and Rosh Chodesh each and every person would come to the Bais HaMikdash to bow before Hashem?
R’ Avraham ben Meir, Ibn Ezra zt”l explains that when stating the above, Yeshaya HaNavi specifically used the words "מדי חדש בחדשו" since the word"מדי" has nearly the same meaning as the words "בכל עת" which means whenever. The Ibn Ezra brings a proof to his point by quoting the words of the of the Navi which describes Elisha HaNavi’s frequent trips to the city of Shunam by stating; "ויהי מדי עברו" - “... and whenever he passed by” (Melachim II 4:8). By Elisha the word "מדי" meant whenever and as such it is plausible to say that Yeshaya’s statement had the same connotation.
R’ Chaim Kanievsky zt”l therefore explains that Yeshaya HaNavi surely meant that in the future when Mashiach comes and the Bais HaMikdash will once again be the epicenter of the world, all of Klal Yisroel who will be living in Eretz Yisroel and close to Yerushalayim, will make the trip to the holy temple on Shabbos and Rosh Chodesh as often as they can to bow before Hashem.
May he come speedily and in our days.