6:8 You should tie them as a reminder on your forearm 1 and fasten them as symbols 2 on your forehead.
11:18 Fix these words of mine into your mind and being, 3 and tie them as a reminder on your hands and let them be symbols 4 on your forehead.
1 sn Tie them as a sign on your forearm. Later Jewish tradition referred to the little leather containers tied to the forearms and foreheads as tefillin. They were to contain the following passages from the Torah: Exod 13:1-10, 11-16; Deut 6:5-9; 11:13-21. The purpose was to serve as a “sign” of covenant relationship and obedience.
2 sn Fasten them as symbols on your forehead. These were also known later as tefillin (see previous note) or phylacteries (from the Greek term). These box-like containers, like those on the forearms, held the same scraps of the Torah. It was the hypocritical practice of wearing these without heartfelt sincerity that caused Jesus to speak scathingly about them (cf. Matt 23:5).