וְשַׂמְתֶּם֙ אֶת־דְּבָרַ֣י אֵ֔לֶּה עַל־לְבַבְכֶ֖ם וְעַֽל־נַפְשְׁכֶ֑ם וּקְשַׁרְתֶּ֨ם אֹתָ֤ם לְאוֹת֙ עַל־יֶדְכֶ֔ם וְהָי֥וּ לְטוֹטָפֹ֖ת בֵּ֥ין עֵינֵיכֶֽם׃
이러므로 너희는 나의 이 말을 너희 마음과 뜻에 두고 또 그것으로 너희 손목에 매어 기호를 삼고 너희 미간에 붙여 표를 삼으며
Rashi
ושמתם את דברי AND YE SHALL PLACE MY WORDS [UPON YOUR HEART] — Even after you have been banished make yourselves distinctive by means of My commands: lay Tephillin, attach Mezuzoth to your doorposts, so that these shall not be novelties to you when you return. Similarly does it state, (Jeremiah 31:21) “Set thee up distinguishing marks” (Sifrei Devarim 43:34).
Alshekh
On your mind. If your mind is attached to serving Hashem, there is no fear that you will be drawn after your eyes. Therefore one must first bind tefillin on the arm, next to the heart, and this is referred to as, “on your hand” because the performance of positive mitzvos is connected to the heart. And on your being, that you should accept upon yourselves to give up your lives rather than transgress prohibitions.
Chizkuni
על לבבכם, “in your hearts;” the word על usually translated as “on, above, etc.,” also appears quite a few times as meaning “next to, beside,” the author cites Exodus 40,3 as an example where the Torah writes: וסכותה על הארון, which is translated as: “you shall screen the ark,” i.e. the dividing curtain before or beside the Holy of Holies screens the Ark from view. In our verse the meaning would be that G-d’s word shall always be close to our hearts.