Standing at the foot of Mount Sinai in readiness to receive the Torah, the Jewish people proclaimed that they would first observe all its commandments and subsequently attempt to understand them.  They declared first "we will do" and then "we will understand."

Some of our people maintain that they will begin to observe mitzvot when they understand them.  

The irrationality of this attitude may be understood from the example of the body, which requires a daily intake of food and air.  No amount of thinking, speaking or studying about food and nutrition can substitute for actual consumption.  On the contrary, failure to eat or breathe will even weaken the mental powers of thought and contemplation.  Obviously the correct and healthy approach is not to study nutrition and respiration first, and then practice them, but the reverse.  For while an individual is eating and drinking and breathing -- though he may not fully understand the process involved -- his faculties of study and concentration are strengthened.

The same applies to the soul.  The elements which it requires for sustenance are best known to its Creator, and at Mount Sinai He revealed them to us, informing us that the "air" and "food" vital to our spiritual existence are -- Torah and mitzvot.  Reason dictates that we perform the mitzvot, and then deliberate on their values.  In the meantime, we gain the spiritual and intellectual strength of mitzvot -- performance during the period in which we examine their truth.

The mitzvah of putting on tefillin every weekday, on the hand facing the heart, and on the head (the seat of the intellect) epitomizes the true Jewish approach: Performance first (hand), with sincerity and whole-heartedness, followed by intellectual comprehension (head).