Adapted from the writings of Dayan Yitzhak Grossman December 3, 2020 All’s well that ends…
Excerpted and adapted from a shiur by Rav Moshe Zev Granek
August 5, 2020
…And to serve Him with all your heart and with all your soul.
The Rambam (Sefer Hamitzvos, Asei 5 and Hil. Tefilah 1:1) writes that the words “and to serve Him with all your heart“ are the source for the mitzvah to daven every day, as the Gemara (Ta’anis 2a) states that avodah shebaleiv refers to tefilah. The Ramban (Hasagos to Sefer Hamitzvos) holds that the Biblical mitzvah applies only during an eis tzarah (emergency).
It is unclear how the Rambam derived that the one must daven every day mid’Oreisa, as this is not explicit in the pesukim he cites. The Seder Hamishnah suggests the following general principle: Whenever the Torah does not specify how often a mitzvah should be performed, it means it must be done once a day. One of the proofs he cites is the mitzvah of tefillin.
However, this proof is questionable, because the Tur and Shulchan Aruch write that the mitzvah of tefillin in principle applies during the entire day, though today we are lenient due to the difficulty involved in maintaining a guf naki (clean body) and avoiding hesech hada’as (loss of concentration). (See Pri Megadim, Aishel Avraham 37:2, who discusses this.)
In addition, it seems that the P’nei Yehoshua (Berachos 21a) did not accept this principle, as he interprets the Gemara as entertaining the notion that one must daven whenever possible, if not for a pasuk that limits it to three times a day.