The 12th principle of faith is that we believe that Moshiach will come. The Brisker Rov explained that we must not only believe that Moshiach will come, we must believe that Moshiach will come TODAY!! As the nusach of the siddur says:
This means that one must believe that it could very well be, that TODAY is the day!
"..... ואע"פ שיתמהמה עם כל זה אחכה לו בכל יום שיבוא."
This means that one must believe that it could very well be, that TODAY is the day!
Rav Moshe Mordechai Schulzinger ztz"l discusses this at length and it is printed in his sefer Mishmar Halevi in many places [עי' משמר הלוי על תמורה סי' ק"ז ועוד ועוד].
The PROBLEM is that the Rambam in his formulation of this principle NEVER SAYS that we have to believe that he can today today - just that eventually he will come. The nusach in the siddur [and the song] doesn't accurately reflect the words of the Rambam.
Here is the lashon haRambam:
No mention of בכל יום שיבוא. Just that he will come.
In addition - the nusach in the siddur could be understood to mean that we must believe every day - that Moshiach will come at some point. But not that we believe that he will come today.
Incidentally, the nusach in the siddur omits the very important detail that we also must believe that Moshiach will come from Beis Dovid and Zera Shlomo. Why?
Also - this places into question the principle of Rabbeinu Chaim Ha-levi Sloveitchik that even if one is shogeg in one of the 13 principles, he loses his portion in the world to come and is not part of Klal Yisrael. Since the vast majority of Jews, even frum Jews [and certainly women and children], don't actively believe that Moshiach MUST come from Beis Dovid and Zera Shlomo - because they simply are ignorant of this fact - that places a large number of good people outside the pale.
וכל זה צריך עיון ובירור ואקוה בל"נ לחזור ולשנות פרק זה ברצות ה' דרכינו!
