In Rabbinic literature we do not find the term בר עונש in the singular. It always appears as בר עונשין - in the plural. The phrase בר מצוה, though, almost always appears only in the singular form. Perhaps this can be explained in terms of the well-known anecdote about the Kotzker Rebbe, who, when asked which was his favorite and most important Mitzvah, replied:
“Whichever Mitzvah I happen to be doing at the time!”
This insight may be of help to a Bar Mitzvah to remind him that, even though he is obligated to fulfill all of the Mitzvos, whatever mitzvah he is fulfilling should be as beloved to him as if it were the only one, he had the Zechus to fulfill. He has only one mitzvah - the one he is doing!
וז"ש חז"ל ]שבת קכז.[ גדולה הכנסת אורחים וכו', שאף שהיה יכול לעלות מעלה בקבלת פני השכינה היה חביב עליו מצוה זו להכניס אורחים ולהעלותם. והיינו דכתיב והוא עומד עליהם ובסוף הפסוק ואברהם עודנו עומד שהיה במדרגת עמידה כנ"ל: ספר פנים יפות
And so, we see in the Gemoroh in Shabbos "Greater is the Mitzvah of Hachnosas Orchim than Mikabel [Greeting] The Shechinah". From here we learn that every Mitzvah has its respect, our obligation, pride, & strength to fulfill in its entirety.
