There is another rationale why service motivated by fear is not sufficient and service motivated by love is necessary. The term avodah (עבודה), translated as "service," relates to the word ibud (עיבוד), which refers to the process of treating a hide so that parchment can be made from it. The process of treating a hide to make parchment requires various activities that involve much difficulty and toil until an animal hide is [sufficiently] processed to be fit to be used as parchment to write passages [for tefillin or a Torah scroll]. Similarly, our Divine service requires comparable difficulty and toil.1

As such, it is apparent that Divine service motivated by fear does not constitute the true nature of avodah. For the attainment of fear does not absolutely require strenuous labor and toil. As mentioned above, there are those who possess a natural tendency for yiras Shamayim,the fear of Heaven, [and attain it without great effort]. Therefore, it is necessary that a person carry out Divine service motivated by love, for this requires strenuous toil and labor.

Thus it is apparent that the command "And you shall serve G‑d your L‑rd" applies both to service motivated by fear — the initial stages of service — and service motivated by love, for as explained in Kuntres HaAvodah,recycle endnote XXII the ultimate level of Divine service is motivated by both fear and love.

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; love does. Thus the command "And you shall serve G‑d your L‑rd" obligates serving G‑d with both love and fear.