Our Rabbis taught: We testify that so-and-so is liable to forty lashes, and they were found to be scheming [conspiring] witnesses. They receive eighty lashes, on account of "You shall not bear false witness" and on account of "You shall do to him as he schemed to do" (Deuteronomy 19:19); these are the words of Rabbi Meir. But the Sages say, they receive only forty. As for the Rabbis, what do they derive from this verse "You shall not bear false witness against your neighbor"? A warning against scheming witnesses. And Rabbi Meir, from where does he derive the warning against scheming witnesses? He derives it from "And those who remain shall hear and fear" (Deuteronomy 19:20). And the Rabbis? That verse they need for the public proclamation. And Rabbi Meir? The proclamation is derived from "shall hear and fear." How were the Ten Commandments given? Five on one tablet and five on the other tablet. It is written "I am the LORD your God," and opposite it "You shall not murder." Scripture tells you that whoever sheds blood, Scripture reckons it to him as though he diminished the divine likeness. A parable: a king of flesh and blood who entered a province, and they set up busts of him and made images of him and struck coins with his likeness. After a time they overturned his busts, broke his images, and invalidated his coins, and so diminished the likeness of the king. So too whoever sheds blood, Scripture reckons it to him as though he diminished the likeness, as it is said "Whoever sheds the blood of man" and so forth, and it is written "for in the image of God He made man" (Genesis 9:6). It is written "You shall have no other gods," and opposite it "You shall not commit adultery." Scripture tells you that whoever worships idols, Scripture reckons it to him as though he committed adultery against the Omnipresent, as it is said "the adulterous wife" and so forth (Ezekiel 16:32), and "The LORD said to me: Go again, love a woman" and so forth (Hosea 3:1). It is written "You shall not take [the LORD's name in vain]" (verse 7), and opposite it is written "You shall not steal." Scripture tells you that whoever steals will in the end come to swear falsely, as it is said "Will you steal, murder, and commit adultery and swear falsely?" (Jeremiah 7:9), and it says "Swearing and lying and murdering" (Hosea 4:2). It is written "Remember the Sabbath day," and opposite it "You shall not bear false witness." Scripture tells you that whoever profanes the Sabbath testifies before the Holy One, blessed be He, that He did not create His world in six days and did not rest on the seventh day; and whoever keeps the Sabbath testifies before the Omnipresent that He created His world in six days and rested on the seventh, as it is said "You are My witnesses, says the LORD, and I am God" (Isaiah 43:12). It is written "Honor your father" (verse 12), and opposite it is written "You shall not covet." Scripture tells you that whoever covets will in the end beget a son who curses his own father and honors one who is not his father. Therefore the Ten Commandments were given five on this tablet and five on that tablet. [And the Sages say: ten on this tablet and ten on that tablet,] as it is said "These words the LORD spoke to all your assembly" and so forth (Deuteronomy 5:19), and it says "Your two breasts are like two fawns" (Song of Songs 4:5), and it says "His hands are rods of gold" and so forth (Song of Songs 5:14). One verse says "You shall not covet," and another verse says "You shall not desire" (Deuteronomy 5:18). How can these two verses be reconciled? This is a warning even against one who only schemes to follow after the object of his craving.
Why the Ten Commandments Were Paired Across Two Tablets
Yalkut Shimoni on Torah 299:1
שָׁנוּ רַבּוֹתֵינוּ, מְעִידִים אָנוּ אֶת אִישׁ פְּלוֹנִי שֶׁהוּא חַיָּב מַלְקוֹת אַרְבָּעִים, וְנִמְצְאוּ זוֹמְמִין, לוֹקִין שְׁמוֹנִים, מִשּׁוּם לֹא תַעֲנֶה, וּמִשּׁוּם "וַעֲשִׂיתֶם לוֹ כַּאֲשֶׁר זָמַם", דִּבְרֵי רַבִּי מֵאִיר, וַחֲכָמִים אוֹמְרִים, אֵין לוֹקִין אֶלָּא אַרְבָּעִים. וְרַבָּנָן, הַאי לֹא תַעֲנֶה בְּרֵעֲךָ מַאי דְּרַשׁ לֵיהּ, אַזְהָרָה לְעֵדִים זוֹמְמִין. ורַבִּי מֵאִיר אַזְהָרָה לְעֵדִים זוֹמְמִין מִנָּא לֵיהּ, נַפְקָא לֵיהּ (שם, כ) מֵ"וְּהַנִּשְׁאָרִים יִשְׁמְעוּ וְיִרָאוּ". וְרַבָּנָן, הַהוּא מִבַּעְיָא לֵיהּ לְהַכְרָזָה. ורַבִּי מֵאִיר, הַכְרָזָה מִ"יִּשְׁמְעוּ וְיִרָאוּ" נַפְקָא. כֵּיצַד נִתְּנוּ עֲשֶׂרֶת הַדִּבְּרוֹת, חֲמִשָּׁה עַל לוּחַ אֶחָד וַחֲמִשָּׁה עַל לוּחַ אֶחָד. כִּתִיב אָנֹכִי ה' אֱלֹהֶיךָ, וּכְנֶגְדּוֹ לֹא תִרְצַח. מַגִּיד הַכָּתוּב שֶׁכָּל מִי שֶׁהוּא שׁוֹפֵךְ דָּמִים מַעֲלֶה עָלָיו הַכָּתוּב כְּאִלּוּ מְמַעֵט בַּדְּמוּת. מָשָׁל לְמֶלֶךְ בָּשָׂר וָדָם שֶׁנִּכְנַס לִמְדִינָה, וְהֶעֱמִיד לוֹ אִיקוֹנוֹת וְעָשׂוּ לוֹ צְלָמִים, וְטָבְעוּ מַטְבְּעוֹת, לְאַחַר זְמַן כִּיפוּ אִיקוֹנוֹת, שָׁבְרוּ צַלְמוֹתָיו, וּפָסְלוּ מַטְבְּעוֹתָיו, וּמִעֲטוּ בִּדְמוּתוֹ שֶׁל מֶלֶךְ, כָּךְ כָּל מִי שֶׁהוּא שׁוֹפֵךְ דָּמִים מַעֲלֶה עָלָיו הַכָּתוּב כְּאִלּוּ מְמַעֵט בַּדְּמוּת, שֶׁנֶּאֱמַר (בראשית ט, ו) "שֹׁפֵךְ דַּם הָאָדָם" וְגוֹ' וּכְתִיב (שם) "כִּי בְצֶלֶם אֱלֹהִים עָשָׂה אֶת הָאָדָם". כְּתִיב לֹא יִהְיֶה לְךָ, וּכְנֶגְדּוֹ לֹא תִנְאָף, מַגִּיד הַכָּתוּב שֶׁכָּל מִי שֶׁהוּא עוֹבֵד עֲבוֹדַת אֱלִילִים מַעֲלֶה עָלָיו הַכָּתוּב כְּאִלּוּ מְנָאֵף מֵאַחֲרֵי הַמָּקוֹם, שֶׁנֶּאֱמַר (יחזקאל טז, לב) "הָאִשָּׁה הַמְנָאָפֶת" וְגוֹ', (הושע ג, א) "וַיֹּאמֶר ה' אֵלַי עוֹד לֵךְ אֱהַב אִשָּׁה" וְגוֹ'. כְּתִיב (פסוק ז) "לֹא תִשָּׂא", וּכְנֶגְדּוֹ כְּתִיב לֹא תִגְנֹב, מַגִּיד הַכָּתוּב שֶׁכָּל מִי שֶׁהוּא גּוֹנֵב סוֹפוֹ לָבֹא לִידֵי שְׁבוּעַת שָׁוְא, שֶׁנֶּאֱמַר "הֲגָנֹב רָצֹחַ וְנָאֹף וְהִשָּׁבֵע לַשֶּׁקֶר", וְאוֹמֵר (הושע ד, ב) "אָלֹה וְכַחֵשׁ וְרָצֹחַ". כְּתִיב זָכוֹר אֶת יוֹם הַשַּׁבָּת, וּכְנֶגְדּוֹ לֹא תַעֲנֶה, מַגִּיד הַכָּתוּב שֶׁכָּל מִי שֶׁהוּא מְחַלֵּל שַׁבָּת, מֵעִיד לִפְנֵי הַקָּדוֹשׁ בָּרוּךְ הוּא שֶׁלֹּא בָּרָא עוֹלָמוֹ לְשִׁשָּׁה יָמִים, וְלֹא נָח בַּיּוֹם הַשְּׁבִיעִי, וְכָל מִי שֶׁהוּא מְשַׁמֵּר אֶת הַשַּׁבָּת, מֵעִיד לִפְנֵי הַמָּקוֹם שֶׁבָּרָא עוֹלָמוֹ לְשִׁשָּׁה יָמִים, וְנָח בַּשְּׁבִיעִי, שֶׁנֶּאֱמַר (ישעיה מג, יב) "אַתֶּם עֵדַי נְאֻם ה' וַאֲנִי אֵל". כְּתִיב (פסוק יב) כַּבֵּד אֶת אָבִיךָ, וּכְנֶגְדּוֹ כְּתִיב לֹא תַחְמֹד, מַגִּיד הַכָּתוּב שֶׁכָּל מִי שֶׁהוּא חוֹמֵד סוֹף שֶׁיִּהְיֶה מוֹלִיד בֵּן מְקַלֵּל לְאָבִיו, וּמְכַבֵּד שֶׁאֵינוֹ אָבִיו, לְכָךְ נִתְּנוּ עֲשֶׂרֶת הַדִּבְּרוֹת חֲמִשָּׁה עַל לוּחַ זֶה, וַחֲמִשָּׁה עַל לוּחַ זֶה. [וַחֲכָמִים אוֹמְרִים עֲשָׂרָה עַל לוּחַ זֶה וַעֲשָׂרָה עַל לוּחַ זֶה] שֶׁנֶּאֱמַר "אֶת הַדְּבָרִים הָאֵלֶּה דִּבֵּר ה' אֶל כָּל קְהַלְכֶם" וְגוֹ', וְאוֹמֵר (שה"ש ד, ה) "שְנֵי שָׁדַיִךְ כִּשְׁנֵי עֳפָרִים", וְאוֹמֵר (שם ה, יד) "יָדָיו גְּלִילֵי זָהָב" וְגוֹ'. כָּתוּב אֶחָד אוֹמֵר לֹא תַחְמֹד, וְכָתוּב אֶחָד אוֹמֵר (דברים ה, יח) "לֹא תִתְאַוֶּה", כֵּיצַד יִתְקַיְּימוּ שְנֵי כְּתוּבִים הַלָּלוּ, הֲרֵי זֶה אַזְהָרָה לְעוֹקֵב אַחַר הַמְּנַאֵף.