You shall observe My statutes and My ordinances,
which a man shall do and live by them.
I am the L-rd.
The phrase "which a man shall do and live by them," can also be read, "in order to imbue life-force within them," implying that not only do G-d's commandments enhance our lives; by observing them we bring them to life. For example, even the most meticulously crafted tefillin cannot accomplish their purpose--thereby effecting a positive change in reality--until a Jewish man wears them.
We are thus the catalyst that brings G-d's plan for creation to fruition, through fulfilling His commandments. In order to "enliven" G-d's commandments, we ourselves must be "alive," i.e., healthy, strong, happy, enthusiastic and optimistic.
--From Kehot's Chumash Vayikra