There are various times in the written Torah that it is quite obvious that what was written was merely the tip of the iceberg and myriads of detailed Torah law was given alongside it. This is the proofs to those naysayers who do not want to buckle down and live according to our Oral Torah traditions.
An example would be in this week’s Torah portion, in a verse that talks about the Tefillin, the adornments that Jewish men wear between their eyes.
The proof of oral Torah being from Sinai is that certain mitzvos don’t tell the details—obviously details were given and we keep them. So the verse in this week’s portion says, “you should tie them for a sign on your hands and be as a decoration between your eyes…” What is the passuk referring to when it says tie “them”? How should you tie them? Which hand? Decorate between your eyes – temporary tattoo or an inset jewel? But every Jew worth his salt, since the time of Sinai has been wearing very exact Tefillin. Color, size, what is written, how it is wrapped, etc. has been given and done through the ages. No one has red Tefillin that is wrapped with tzititis strings around the palm. No one ever questioned that the Oral law that we have is “Toras Moshe mee’sinai” that we were told, along with these verses exactly how to keep the verses.