The Rambam (Hilchos Melochim 11:1) denounces one who does not await the arrival of Moshiach:
וכל מי שאינו מאמין בו או מי שאינו מחכה לביאתו לא בשאר נביאים בלבד הוא כופר אלא בתורה ומשה רבינו שהרי תורה העידה עליו שנ' ושב ה א 'לקיך את שבותך ורחמך ושב וקבצך מכל העמים וכו ' אם יהיה נדחך בקצה השמים משם יקבצך ה' אלקיך ומשם יקחך והביאך ה' אלקיך.
“Anyone who does not believe in him or does not await his coming, denies not only the statements of the other prophets, but those of the Torah and Moshe Rabbeinu. The Torah testified to his coming (Devorim 30:3-5) “G-d will bring back your captivity and have mercy upon you. He will again gather you from among the nations... Even if your Diaspora is at the ends of the heavens, G-d will gather you up from there... and bring you to the land....”
The Rambam uses very harsh words to describe a Jew who does not await the arrival of Moshiach. He calls him nothing short of a heretic, who is a kofer [denier] in the Torah and Moshe Rabbeinu.
The Rambam compiled what he refers to as the Shlosh Asar Ikkarim, the Thirteen Fundamental Principles of the Jewish faith, as derived from the Torah (which can be found in the Rambam’s introduction to Perek Chelek, and in most siddurim after Shacharis). These are the fundamental truths of our religion and its very foundations. The twelfth one is:
אני מאמין באמ ונה שלמה בביאת המשיח ואף על פי שיתמהמה עם כל זה אחכה לו בכל יום שיבא.
“I believe with complete faith in the arrival of Moshiach. Even though there has already been a big delay, I nevertheless wait for him every day to come.”
