Text of the Mezuzah
(13) If, then, you obey the commandments that I enjoin upon you this day, loving the LORD your God and serving Him with all your heart and soul, (14) I will grant the rain for your land in season, the early rain and the late. You shall gather in your new grain and wine and oil— (15) I will also provide grass in the fields for your cattle—and thus you shall eat your fill. (16) Take care not to be lured away to serve other gods and bow to them. (17) For the LORD’s anger will flare up against you, and He will shut up the skies so that there will be no rain and the ground will not yield its produce; and you will soon perish from the good land that the LORD is assigning to you. (18) Therefore impress these My words upon your very heart: bind them as a sign on your hand and let them serve as a symbol on your forehead, (19) and teach them to your children—reciting them when you stay at home and when you are away, when you lie down and when you get up; (20) and inscribe them on the doorposts of your house and on your gates— (21) to the end that you and your children may endure, in the land that the LORD swore to your fathers to assign to them, as long as there is a heaven over the earth.
Why were these passages chosen to be in the mezuzah?
(יג) חַיָּב אָדָם לְהִזָּהֵר בִּמְזוּזָה מִפְּנֵי שֶׁהִיא חוֹבַת הַכּל תָּמִיד. וְכָל זְמַן שֶׁיִּכָּנֵס וְיֵצֵא יִפְגַּע בְּיִחוּד הַשֵּׁם שְׁמוֹ שֶׁל הַקָּדוֹשׁ בָּרוּךְ הוּא וְיִזְכֹּר אַהֲבָתוֹ וְיֵעוֹר מִשְּׁנָתוֹ וְשִׁגְיוֹתָיו בְּהַבְלֵי הַזְּמַן. וְיֵדַע שֶׁאֵין דָּבָר הָעוֹמֵד לְעוֹלָם וּלְעוֹלְמֵי עוֹלָמִים אֶלָּא יְדִיעַת צוּר הָעוֹלָם. וּמִיָּד הוּא חוֹזֵר לְדַעְתּוֹ וְהוֹלֵךְ בְּדַרְכֵי מֵישָׁרִים. אָמְרוּ חֲכָמִים הָרִאשׁוֹנִים כָּל מִי שֶׁיֵּשׁ לוֹ תְּפִלִּין בְּרֹאשׁוֹ וּבִזְרוֹעוֹ וְצִיצִית בְּבִגְדוֹ וּמְזוּזָה בְּפִתְחוֹ מֻחְזָק הוּא שֶׁלֹּא יֶחֱטָא שֶׁהֲרֵי יֵשׁ לוֹ מַזְכִּירִין רַבִּים וְהֵן הֵם הַמַּלְאָכִים שֶׁמַּצִּילִין אוֹתוֹ מִלַּחֲטֹא שֶׁנֶּאֱמַר (תהילים לד ח) ״חֹנֶה מַלְאַךְ יְיָ׳ סָבִיב לִירֵאָיו וַיְחַלְּצֵם״.
בְּרִיךְ רַחֲמָנָא דְּסַיְּעָן:
(13) A person should pay heed to the precept of the Mezuzah; for it is an obligation perpetually binding upon all. Whenever one enters or leaves a home with the Mezuzah on the doorpost, he will be confronted with the Declaration of God's Unity, blessed be His holy name; and will remember the love due to God, and will be aroused from his slumbers and his foolish absorption in temporal vanities. He will realize that nothing endures to all eternity save knowledge of the Ruler of the Universe. This thought will immediately restore him to his right senses and he will walk in the paths of righteousness. Our ancient teachers said: He who has phylacteries on his head and arm, fringes on his garment and a Mezuzah on his door may be presumed not to sin, for he has many monitors—angels that save him from sinning, as it is said, (Psalms 34:8) "The angel of the Lord encampeth round about them that fear Him and delivereth them".
(ד) מִנְהָג פָּשׁוּט שֶׁכּוֹתְבִים עַל הַמְּזוּזָה מִבַּחוּץ כְּנֶגֶד הָרֶוַח שֶׁבֵּין פָּרָשָׁה לְפָרָשָׁה שַׁדַּי וְאֵין בָּזֶה הֶפְסֵד לְפִי שֶׁהוּא מִבַּחוּץ. אֲבָל אֵלּוּ שֶׁכּוֹתְבִין מִבִּפְנִים שְׁמוֹת הַמַּלְאָכִים אוֹ שֵׁמוֹת קְדוֹשִׁים אוֹ פָּסוּק אוֹ חוֹתָמוֹת הֲרֵי הֵן בִּכְלַל מִי שֶׁאֵין לָהֶם חֵלֶק לָעוֹלָם הַבָּא. שֶׁאֵלּוּ הַטִּפְּשִׁים לֹא דַּי לָהֶם שֶׁבִּטְּלוּ הַמִּצְוָה אֶלָּא שֶׁעָשׂוּ מִצְוָה גְּדוֹלָה שֶׁהִיא יִחוּד הַשֵּׁם שֶׁל הַקָּדוֹשׁ בָּרוּךְ הוּא וְאַהֲבָתוֹ וַעֲבוֹדָתוֹ כְּאִלּוּ הוּא קָמֵעַ שֶׁל הֲנָיַת עַצְמָן כְּמוֹ שֶׁעָלָה עַל לִבָּם הַסָּכָל שֶׁזֶּהוּ דָּבָר הַמְהַנֶּה בְּהַבְלֵי הָעוֹלָם:
(4) It is a universal custom to write the word Shaddai (Almighty) on the other side of the Mezuzah, opposite the blank space between the two sections. As this word is written on the outside, the practice is unobjectionable. They, however, who write names of angels, holy names, a Biblical text or inscriptions usual on seals, within the Mezuzah, are among those who have no portion in the world to come. For these fools not only fail to fulfill the commandment but they treat an important precept that expresses the Unity of God, the love of Him, and His worship, as if it were an amulet to promote their own personal interests; for, according to their foolish minds, the Mezuzah is something that will secure for them advantage in the vanities of the world.**A reproof to those who sell Mezuzoth to be worn as amulets !
Its not allowed because bad spirits come to houses that don't have a mezuzah and when they took the mezuzah from the house its like they afflicted the residence of the house: