Musar על מכות 21:8

When Isaiah 49,3 quotes G–d as saying of Israel: ישראל אשר בך אתפאר, "Israel, you, in whom I glory," the reference may well be to Jacob in his capacity of ישראל סבא who dons the phylacteries of the head. Those phylacteries are known as פאר, as glorious headdress, as is well known. I have already mentioned that the whole Torah is compared to תפילין. Torah itself is subsumed in the word את, which the Talmud in Shabbat 55 understands as referring to people who observe Torah from א-ת. The extra letters את in אתפאר refer to such people.