לאות על ידך – לפי עומק פשוטו: יהיה לך לזכרון תמיד, כאילו כתוב על ידך, כעין: שימני כחותם על לבך (שיר השירים ח׳:ו׳).
בין עיניך – כעין תכשיט ורביד זהב שרגילין ליתן על המצח לנוי.
Rashbam, Rabbi Shmuel ben Meir(12th c.)
"a sign on your hand": According to the deep [understanding] of the text: Let [them] be an eternal reminder, as though they were written on your hand, as in, 'Place me as a sign on your heart.'
Between your eyes - Like jewelry or a gold necklace that they usually wear on the forehead for decoration.
והיה לך לאות על ידך ולזכרון בין עיניך – יתכן על שני פירושים: האחד – על דרך: קשרם על גרגרתיך כתבם על לוח לבך (משלי ג׳:ג׳), ויהי טעם לאות כמו: סימן. ומהו: שיהיה לאות ולזכרון הוא כי ביד חזקה – שתאמר כן בלבך ולבנך. וכן הכתוב השני, והיה לאות על ידכהולטוטפת בין עיניך (שמות י״ג:ט״ז), והוא: כי בחוזק יד הוציאנו י״י ממצרים.
ומלת טוטפת זרה במקרא [ואין לה חבר]. והמכחישים אומרים: כי היא מן: {ו}הטף אל דרום (יחזקאל כ״א:ב׳), [ועוד אפרשנה].
והפירוש השני – להיות כמשמעו, לעשות תפילין שליד ושלראש. ובעבור שהעתיקו כן חכמינו ז״ל, בטל הפירוש הראשון, כי אין עליו עדים נאמנים כאשר יש לפירוש השני.
R. Abraham Ibn Ezra
Let it be a sign on your hand and a reminder between your eyes - This verse can be explained in two ways - The First, according to: Tie them on your neck, inscribe them on the tablet of your heart.
The meaning of the word 'oht' (sign) here is, a symbol...a symbol that God took us out of Egypt with a strong hand...meaning, that you should say this to yourself in your heart and to your children.
The second way, to be what it means, that you should make tefillin for your hand and head. And since our blessed Sages established it this way, the first explanation is void, since there are no faithful testimonies for the second explanation.
-Matthew 23:5
The Gemara cites another aggadic statement: Rabbi Avin bar Rav Adda said that Rabbi Yitzḥak said: From where is it derived that the Holy One, Blessed be He, wears phylacteries? As it is stated: “The Lord has sworn by His right hand, and by the arm of His strength” (Isaiah 62:8). Since it is customary to swear upon holy objects, it is understood that His right hand and the arm of His strength are the holy objects upon which God swore. Specifically, “His right hand” refers to the Torah, as it is stated in describing the giving of the Torah: “From His right hand, a fiery law for His people” (Deuteronomy 33:2). “The arm of His strength,” His left hand, refers to phylacteries, as it is stated: “The Lord gave strength to His nation” (Psalms 29:11), in the form of the mitzva of phylacteries. The Gemara asks: And from where is it derived that phylacteries provide strength for Israel? As it is written: “And all the nations of the land shall see that the name of the Lord is called upon you, and they will fear you” (Deuteronomy 28:10). It was taught in a baraita that Rabbi Eliezer the Great says: This is a reference to the phylacteries of the head, upon which the name of God is written in fulfillment of the verse: “That the name of the Lord is called upon you.” Rav Naḥman bar Yitzḥak said to Rav Ḥiyya bar Avin: What is written in the phylacteries of the Master of the world? Rav Ḥiyya bar Avin replied: It is written: “Who is like Your people, Israel, one nation in the land?” (I Chronicles 17:21). God’s phylacteries serve to connect Him, in a sense, to the world, the essence of which is Israel.
(א) פותחים הארון:
(ב) חזן: - אַנְעִים זְמִירות וְשִׁירִים אֶאֱרוג. כִּי אֵלֶיךָ נַפְשִׁי תַעֲרוג:
...
קהל: - צַח וְאָדום לִלְבוּשׁו אָדום. פּוּרָה בְּדָרְכו בְּבואו מֵאֱדום:
חזן: - קֶשֶׁר תְּפִלִּין הֶרְאָה לֶעָנָיו. תְּמוּנַת ה' לְנֶגֶד עֵינָיו:
...
...God showed God's tefillin knot to Moses (the humble one), the wise one...
Evidence that in France & Spain in 11 and 1200s the mitzvah of tefillin was not practice widely.
Tosafot, post-Rashi commentaries to the Talmud 12th - 15th century.
...many Jews here do not have tefillin...
In what order are these passages placed in the tefillin? Well the Talmud (Menachot 34b) records the tradition on this matter: "Kadesh and V'haya ki yeviacha to the right [of the individual opposite the tefillin wearer1]; Shema and V'haya im shamoa to the left." Furthermore, the Talmud says, if the passages are not in their proper order, the tefillin are not kosher.
The interpretation of this Talmudic rule, however, has been hotly debated.
One opinion is that "Shema and V'haya im shamoa to the left" starts from the center of the tefillin and extends left-wards. This is the opinion championed by Rashi, an eminent 11th century sage.
Rashi's Tefillin:
The other opinion maintains that "Shema and V'haya im shamoa to the left" starts from the left edge of the tefillin and extends inwards. This is the opinion supported by Rashi's grandson, known as "Rabbeinu Tam."
Rabbeinu Tam's Tefillin:
The Code of Jewish Law sides with Rashi's opinion. Nevertheless, it says that "all G‑dfearing individuals"2 should have two pairs of tefillin and wear both each day. In chassidic circles it is especially common to wear two pairs of tefillin, this because according to kabbalah it is important to wear both pairs, each one representing a different divine flow of energy.
(www.chabad.org)
(ג) בָּרוּךְ אַתָּה יְהֹוָה אֱלֹהֵֽינוּ מֶֽלֶךְ הָעוֹלָם אֲשֶׁר קִדְּ֒שָֽׁנוּ בְּמִצְוֹתָיו וְצִוָּנוּ לְהָנִיחַ תְּפִלִּין:
(ד) ויכרוך שבע כריכות סביב זרועו, ואחר כך יניח של ראש בגובה ראשו כנגד בין עיניו, וקודם שמהדקן יברך:
(ה) בָּרוּךְ אַתָּה יְהֹוָה אֱלֹהֵֽינוּ מֶֽלֶךְ הָעוֹלָם אֲשֶׁר קִדְּ֒שָֽׁנוּ בְּמִצְוֹתָיו וְצִוָּנוּ עַל מִצְוַת תְּפִלִּין:
(ו) ואחר שיהדק הרצועה על ראשו יאמר:
(ז) בָּרוּךְ שֵׁם כְּבוֹד מַלְכוּתוֹ לְעוֹלָם וָעֶד:
(3) Blessed are You, Adonoy our God, King of the Universe, Who sanctified us with the commandments and commanded us to put on tefillin.
(4) Wrap the strap around your arm 7 times and then place the “tefillin of the head” on your head above the region between your eyes, and say:
(5) Blessed are You, Adonoy our God, King of the Universe, Who sanctified us with the commandments, and commanded us concerning the mitzvoh of tefillin.
(6) With the “tefillin of the head” in place, say:
(7) Blessed is God's Name, Whose glorious kingdom is forever and ever.