ורצע אדניו את אזנו במרצע (משפטים כא:ו)    

And his master pierced his ear with an awl.

Rashi explains: “The ear that heard on Har Sinai that one isn’t allowed to steal, and did steal, then that ear needs to get pierced.”

We need to understand why is the ear the guilty party. Didn’t the hand steal? But the answer is, if you don’t comply with what you heard, you shouldn’t hear anymore…(חידושי הרי”ם זצ”ל).

Another question is asked.  The commandment “לא תגנוב” from the עשרת הדברות refers to stealing נפשות – lives, so why is he being punished for what Rashi explains ששמעה – what he heard at Har Sinai – if he stole money? Because when Hashem said the ten commandments, He also described the details of each commandment.  For example, לא תגנוב it included not stealing lives, money, etc. (חנוכת התורה).