[Avodah] first mention in the Torah

[Eli Turkel]

<<"We have a tradition that if we wish to discover a concept's meaning, we
should look at the first time it is mentioned in the Torah."

I found the above statement at a fine yeshivah's website. I've heard it
several times, and have seen some interesting examples, but can
someone tell me the source of the tradition, >>

RYBS mentions this principle I believe in the name of his
great-grand-father the Beis HaLevi.

It is a beautiful derasha I have used many times.
At a brit milah we state "hakatan hazeh gadol yehie".
This blessing doesn't make much sense. RYBS explained it based on the
above principle. The first time katan and gadol appear in the Torah is
the description of the moon and sun.
The difference between the moon and sun is that the moon merely
reflects the light of the sun.

Our blessing is that now the infant can only reflect that which is
given to him by his parents so he like the moon. We bless him that
when he grows up he should be like the sun with his own light shining
n the world giving instead of merely reflecting

-- 
Eli Turkel