Likutei Halakhot, Orach Chaim, Laws of Phylacteries 5:4/ליקוטי הלכות·אורח חיים·הלכות תפילין ה׳:ד׳

1And the essence of tefillin Brains are the aspect of life of Holiness, which one attains through tefillin, for the Brains are the Life, as written (Eccl. 7), “Hachokhmah tichyeh/Wisdom preserves alive,” as our Rabbis z”l said (Menachoth 44), “One who lays tefillin attains life, as it says, “Adonai `aleihem yichyu/Adonai, by these things men live” (Isa. 38:16), as brought in the Qawanoth, that tefillin are the aspect of the three names Ehyeh H' Eyheh [21+26+21=68] which are gematria ChaYIM [68], which are the Brains, see there, for the Brains of the tefillin are drawn from the aspect of Tiqunei Diqna Qadisha, as brought in the Qawanoth, as they are the entirety of these holy elders, who have their root in the aforementioned Most Supernal Elder, who is the blind one, who boasted that he lives truly long life, for he is very old and yet he is an utmost suckling babe, and still has not begun to live at all, but nevertheless he is very old, and all the world's time does not amount to him so much as an eyeblink etc. And behold, although these are things that the `Atiq Yomin has covered and thought cannot grasp it at all, and there is no man on earth who can make this interpretation and explain this mystery; nevertheless since by Hashem's compassion on His people these words of his have come out of his holy mouth and they have taken form and been printed in a book, it behooves us to dig and find in them some Remez relevant to the story, such that we may merit waking up from our sleep, which this was his holy intention with these stories that he told, in order to wake up all people who sleep away their days etc., as explained in the Torah ”Pathach R' Shim`on” (LM #60), and there you will see and understand the great wonders of these stories, for they are the aspect of stories of Shanim Qadhmoniyoth/Ancient Years-Faces, the aspect of `Atiq/Ancient, the aspect of Hadhrath Panim/Distinguished Face, from which all the seventy faces of the Torah derive etc.; take a good look there.