Rabbeinu Tam Tefillin

According to the Arizal, donning Rabbeinu Tam Tefillin is a law, not a custom. The question of “custom” is only whether to don them after Rashi Tefillin or at the same time, but the Arizal holds that all Jewish men are obligated to don both pairs.

Additionally, the darkness of exile has become doubled and redoubled, and all agree that today’s “Hamans,” and their threats, are growing… The Sages explain that the verse, “The nations of the world shall see the Name of G-d is upon you, and they shall fear you,” refers to the donning of Tefillin. Therefore, when “G-d’s Name” is increased upon Jews – through Rabbeinu Tam Tefillin, the other nations’ fear of Jews will increase as well.

One cannot point to the actions of the pre-20th century Halachic authorities to excuse oneself from doing so, because they were living in entirely different times: Jews weren’t reading newspapers; they weren’t immersing themselves in secular studies – which, the Alter Rebbe writes in Tanya, “desensitize the mind to G-dliness” unless one utilizes them in the service of G-d. Today’s times demand an increase in the spiritual refinement of the intellect, which is the entire purpose of the Tefillin – “to subjugate the mind and heart to G-d.”