There is another rationale why service motivated by fear is not sufficientוְעוֹד עִנְיָן בָּזֶה שֶׁלֹּא מַסְפִּיק הָעֲבוֹדָה מִיִּרְאָה
and service motivated by love is also necessary.אֶלָּא מֻכְרַחַת לִהְיוֹת גַּם הָעֲבוֹדָה מֵאַהֲבָה,
The term avodah (עבודה), translated as “service,” relates to the word ibud (עיבוד), which refers to the process of treating an animal hide so that parchment or leather can be made from it.דְּהִנֵּה עֲבוֹדָה הִיא מִלְּשׁוֹן עִבּוּד עוֹרוֹת,
The process of treating a hide to make parchment requires various activities that involve much difficulty and toilוּכְשֵׁם שֶׁבְּעִבּוּד עוֹרוֹת יֵשׁ צֹרֶךְ בְּכַמָּה וְכַמָּה פְּעֻלּוֹת הַבָּאוֹת עַל יְדֵי טִירְחָא וִיגִיעָה גְּדוֹלָה
until the hide is sufficiently processed and fit to be used as parchment to write passages for tefillin or a Torah scroll.עַד שֶׁנַּעֲשֶׂה הָעוֹר מְעֻבָּד וְרָאוּי לִהְיוֹת קְלָף שֶׁיִּכְתְּבוּ עָלָיו פָּרָשִׁיּוֹת כוּ',
Similarly, our Divine service requires labor –כְּמוֹ כֵן צְרִיכָה לִהְיוֹת עֲבוֹדַת ה' בְּאֹפֶן שֶׁל עֲבוֹדָה דַּוְקָא,
The person’s processes of thinking and feeling (the powers of his soul in chassidic terminology) are the analogue to the hide that is treated in the tanning process.
comparably great difficulty and toil.טִירְחָא וִיגִיעָה גְּדוֹלָה.
As such, it is apparent that Divine service motivated by fear does not constitute the true nature of avodah.וּמִזֶּה מוּבָן שֶׁהָעֲבוֹדָה מִיִּרְאָה אֵינָהּ אֲמִתִּית עִנְיַן הָעֲבוֹדָה,
For the attainment of fear does not necessarily require strenuous labor and toil.כִּי, בַּיִּרְאָה אֵין הֶכְרֵחַ שֶׁתִּהְיֶה עֲבוֹדָה וִיגִיעָה גְּדוֹלָה,
As mentioned above, there are those who possess a natural tendency for yiras Shamayim, the fear of Heaven, and attain it without great effort.וּכְנִזְכָּר לְעֵיל שֶׁיֶּשְׁנָם כָּאֵלֶּה שֶׁיֵּשׁ לָהֶם יִרְאַת שָׁמַיִם טִבְעִית כוּ',
Therefore, it is necessary that a person carry out Divine service motivated by love,וְלָכֵן בְּהֶכְרֵחַ לִהְיוֹת גַּם הָעֲבוֹדָה מֵאַהֲבָה,
for this can only be acheived through strenuous toil and labor.שֶׁבָּאָה עַל יְדֵי עֲבוֹדָה וִיגִיעָה גְּדוֹלָה דַּוְקָא.
For transforming a person’s natural tendencies from the desire for material satisfaction to the desire for holiness is an extended process. Even a person who possesses a natural tendency for yiras Shamayim, the fear of Heaven, also possesses natural desires for material satisfaction, and those natural desires can be transformed to holiness only through love.
Thus it is apparent that the command “And you shall serve G‑d your L-rd”וּמִזֶּה מוּבָן שֶׁמַּה שֶּׁכָּתוּב "וַעֲבַדְתֶּם אֵת הֲוָיָ׳ אֱלֹקֵיכֶם",
applies to both service motivated by fearקָאֵי הֵן עַל הָעֲבוֹדָה מִיִּרְאָה
– the initial stages of service –שֶׁהִיא רֵאשִׁית הָעֲבוֹדָה,
and service motivated by love,וְהֵן עַל הָעֲבוֹדָה מֵאַהֲבָה,
for as explained in Kuntres HaAvodah,1 the ultimate level of Divine service is motivated by both fear and love.וְכַמְּבֹאָר בְּקוּנְטְרֵס הָעֲבוֹדָה שֶׁשְּׁלֵמוּת הָעֲבוֹדָה הִיא הֵן מִיִּרְאָה וְהֵן מֵאַהֲבָה.

Summary

Avodah (עבודה), “service,” relates to the word ibud (עיבוד), which refers to the process of treating a hide so that parchment can be made from it. This process – and similarly, our Divine service – requires strenuous labor and toil. Now fear of G‑d does not necessarily require such arduous efforts as does love. Thus the command “And you shall serve G‑d your L-rd” obligates serving G‑d with both love and fear.