Tefillin, technically called Phylacteries in English, are black leather boxes and straps that Jewish men tie around their head and arms during prayer, because this is as close as they can get to expressing their love of leather, the kinky motherfuckers.
Inside each Tefillin box is a scroll with certain important texts hand written by a Jewish calligrapher, or Sofer. These texts remind the wearer to love God very very much, and to put their life on the line for God if they are called to do so.
These scrolls are sealed into the boxes, so the wearer can’t actually read what’s written on the scrolls. But then again they are wearing each scroll twice, so you could argue that two scrolls that you can’t read are better than one that you can.