L’kovod the Bar-Mitzvah of Binyamin Yitzchak Weinblatt:
Chazal tell us that although B’nei Yisrael’s na’aseh v’nishma was considered a special declaration of acceptance of Torah and mitzvohs, nevertheless, it was missing an element of joy and willingness, which only came about much much later, as a result of the yeshu’ah of the events of Purim.
So, too, as every Bar-Mitzvah boy accepts the ohl of mitzvohs, he should remember that, as he says in his first ma’ariv:
“And we should be joyful with the words of Your Torah and Your mitzvohs forever and ever”
ונשמח בדברי תורתיך ובמצוותיך לעולם ועד
He should remember to be joyful and excited at the thought of taking his place as a full-fledged member of HaShem’s loyal army.