Ve Etchanan : What is love?
Mass Revelation Theory

(לב) כִּי שְׁאַל נָא לְיָמִים רִאשֹׁנִים אֲשֶׁר הָיוּ לְפָנֶיךָ לְמִן הַיּוֹם אֲשֶׁר בָּרָא אֱלֹהִים אָדָם עַל הָאָרֶץ וּלְמִקְצֵה הַשָּׁמַיִם וְעַד קְצֵה הַשָּׁמָיִם הֲנִהְיָה כַּדָּבָר הַגָּדוֹל הַזֶּה אוֹ הֲנִשְׁמַע כָּמֹהוּ.

(לג) הֲשָׁמַע עָם קוֹל אֱלֹהִים מְדַבֵּר מִתּוֹךְ הָאֵשׁ כַּאֲשֶׁר שָׁמַעְתָּ אַתָּה וַיֶּחִי.

(32) For ask now of the days past, which were before thee, since the day that God created man upon the earth, and from the one end of heaven unto the other, whether there hath been any such thing as this great thing is, or hath been heard like it?

(33) Did ever a people hear the voice of God speaking out of the midst of the fire, as thou hast heard, and live?

Who Can Hear God's Voice and Live?

(כא) וַתֹּאמְרוּ הֵן הֶרְאָנוּ יקוק אֱלֹהֵינוּ אֶת כְּבֹדוֹ וְאֶת גָּדְלוֹ וְאֶת קֹלוֹ שָׁמַעְנוּ מִתּוֹךְ הָאֵשׁ הַיּוֹם הַזֶּה רָאִינוּ כִּי יְדַבֵּר אֱלֹהִים אֶת הָאָדָם וָחָי.

(21) and ye said: ‘Behold, the LORD our God hath shown us His glory and His greatness, and we have heard His voice out of the midst of the fire; we have seen this day that God doth speak with man, and he liveth.

Only God Exists
(לה) אַתָּה הָרְאֵתָ לָדַעַת כִּי יקוק הוּא הָאֱלֹהִים אֵין עוֹד מִלְבַדּוֹ.
(35) Unto thee it was shown, that thou mightiest know that the LORD, He is God; there is none else beside Him.
non- Existince of the world
(לט) וְיָדַעְתָּ הַיּוֹם וַהֲשֵׁבֹתָ אֶל לְבָבֶךָ כִּי יקוק הוּא הָאֱלֹהִים בַּשָּׁמַיִם מִמַּעַל וְעַל הָאָרֶץ מִתָּחַת אֵין עוֹד.
(39) know this day, and lay it to thy heart, that the LORD, He is God in heaven above and upon the earth beneath; there is none else.
(ד) וְאַתֶּם הַדְּבֵקִים בַּיקוק אֱלֹהֵיכֶם חַיִּים כֻּלְּכֶם הַיּוֹם.
(4) But ye that did cleave unto the LORD your God are alive every one of you this day.
The Wedding

(ד) שְׁמַע:יִשְׂרָאֵל יקוק , אֱלֹהֵינוּ יקוק, אֶחָד.

(4) HEAR, O ISRAEL: THE LORD IS OUR GOD, THE LORD IS ONE.
In Love

(ה) וְאָהַבְתָּ אֵת יקוק אֱלֹהֶיךָ בְּכָל לְבָבְךָ וּבְכָל נַפְשְׁךָ וּבְכָל מְאֹדֶךָ. (ו) וְהָיוּ הַדְּבָרִים הָאֵלֶּה אֲשֶׁר אָנֹכִי מְצַוְּךָ הַיּוֹם עַל לְבָבֶךָ.

(ז) וְשִׁנַּנְתָּם לְבָנֶיךָ וְדִבַּרְתָּ בָּם בְּשִׁבְתְּךָ בְּבֵיתֶךָ וּבְלֶכְתְּךָ בַדֶּרֶךְ וּבְשָׁכְבְּךָ וּבְקוּמֶךָ. (ח) וּקְשַׁרְתָּם לְאוֹת עַל יָדֶךָ וְהָיוּ לְטֹטָפֹת בֵּין עֵינֶיךָ. (ט) וּכְתַבְתָּם עַל מְזוּזֹת בֵּיתֶךָ וּבִשְׁעָרֶיךָ.

(5) And thou shalt love the LORD thy God with all thy heart, and with all thy soul, and with all thy might. (6) And these words, which I command thee this day, shall be upon thy heart; (7) and thou shalt teach them diligently unto thy children, and shalt talk of them when thou sittest in thy house, and when thou walkest by the way, and when thou liest down, and when thou risest up. (8) And thou shalt bind them for a sign upon thy hand, and they shall be for frontlets between thine eyes. (9) And thou shalt write them upon the door-posts of thy house, and upon thy gates.

Mishnah Torah - Madda : Teshuvah

Halacha 2

One who serves [God] out of love occupies himself in the Torah and the mitzvot and walks in the paths of wisdom for no ulterior motive: not because of fear that evil will occur, nor in order to acquire benefit. Rather, he does what is true because it is true, and ultimately, good will come because of it.

This is a very high level which is not merited by every wise man. It is the level of our Patriarch, Abraham, whom God described as, "he who loved Me," for his service was only motivated by love.

God commanded us [to seek] this rung [of service] as conveyed by Moses as [Deuteronomy 6:5] states: "Love God, your Lord.'' When a man will love God in the proper manner, he will immediately perform all of the mitzvot motivated by love.

Halacha 3

What is the proper [degree] of love? That a person should love God with a very great and exceeding love until his soul is bound up in the love of God. Thus, he will always be obsessed with this love as if he is lovesick.

[A lovesick person's] thoughts are never diverted from the love of that woman. He is always obsessed with her; when he sits down, when he gets up, when he eats and drinks. With an even greater [love], the love for God should be [implanted] in the hearts of those who love Him and are obsessed with Him at all times as we are commanded [Deuteronomy 6:5: "Love God...] with all your heart and with all soul."

This concept was implied by Solomon [Song of Songs 2:5] when he stated, as a metaphor: "I am lovesick." [Indeed,] the totality of the Song of Songs is a parable describing [this love].