Exodus 13:16 Halakhah: Contemporary Halakhic Problems, Vol III & Sefer HaChinukh

There is no substitute for the prayer of the community as a unified whole. As so eloquently stated by Ramban in his commentary on Exodus 13:16, "The purpose of … synagogues and the merit of communal prayer is that people have a place wherein they assemble and express gratitude to the Almighty … and proclaim publicly and say before him 'we are Your creatures!' " To this end Jews, men and women alike, join together in the synagogue in common and collective expression of worship and devotion.

And he first places that of the arm and afterwards that of the head; and when he removes them, he removes that of the head first. And [also] that which they said (Berakhot 9b, (Mishneh Torah, Laws of Tefillin, Mezuzah and the Torah Scroll 4:10) that the time of tefillin during the day is from when one can see his friend until the sun sets, as it is stated (Exodus 13:10), "You shall observe this statute in its proper time from day to day" - and "this statute" is the commandment of tefillin. And Shabbat and holidays - and the same is true of the intermediate festival days - are not a time for the placing of tefillin, as it is stated about them (Exodus 13:16), "And it shall be a sign." And Shabbat days and holidays are a sign themselves, and we do not need another sign.